util/e6400-flash-unlock: Update to upstream version

This updates lbmk's copy of e6400-flash-unlock to commit c5567fece479
(README.md: Update with info about broader device support) in my
upstream repo.

Changes:
- Theoretical support for any Dell system that implements that flash
  descriptor override command. This is done by reading base address
  registers at runtime instead of hard coding them for specific devices.
  Tested on the Latitude E6400 and Latitude E6430.
- Support for OpenBSD. It compiles, runs, and behaves as expected,
  though I have not actually tested internally flashing with flashrom
  yet. It should work though, as the program checks if the descriptor
  override is set and the BIOS Write Enable is able to be set to 1, which
  is all that is needed to internal flash.
- Integrated changes made in the lbmk copy
- Moved operating system accessor implementations to their own file

It should be fully functional, though minor formatting and cleanup
changes are still planned.

Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>

util/e6400-flash-unlock/README.md

@@ -1,13 +1,44 @@
-# Dell Latitude E6400 Internal Flashing
+# Dell Laptop Internal Flashing
 
 This utility allows you to use flashrom's internal programmer to program the
 entire BIOS flash chip from software while still running the original Dell
-BIOS, which normally restricts software writes to the flash chip.
+BIOS, which normally restricts software writes to the flash chip. It seems like
+this works on any Dell laptop that has an EC similar to the SMSC MEC5035 on the
+E6400, which mainly seem to be the Latitude and Precision lines starting from
+around 2008 (E6400 era).
 
 ## TL;DR
 Run `make` to compile the utility, and then run `sudo ./e6400_flash_unlock` and
 follow the directions it outputs.
 
+## Confirmed supported devices
+- Latitude E6400
+- Latitude E6410
+- Latitude E4310
+- Latitude E6430
+- Precision M6800
+
+It is likely that any other Latitude/Precision laptops from the same era as
+devices specifically mentioned in the above list will work as Dell seems to use
+the same ECs in one generation.
+
+## Detailed device specific behavior
+- On GM45 era laptops, the expected behavior is that you will run the utility
+  for the first time, which will tell the EC to set the descriptor override on
+  the next boot. Then you will need to shut down the system, after which the
+  system will automatically boot up. You should then re-run the utility to
+  disable SMM, after which you can run flashrom. Finally, you should run the
+  utility a third time to reenable SMM so that shutdown works properly
+  afterwards.
+- On 1st Generation Intel Core systems such as the E6410 and newer, run the
+  utility and shutdown in the same way as the E6400. However, it seems like the
+  EC no longer automatically boots the system. In this case you should manually
+  power it on. It also seems that the firmware does not set the BIOS Lock bit
+  when the descriptor override is set, making the 2nd run after the reboot
+  technically unnecessary. There is no harm in rerunning it though, as the
+  utility can detect when the flash is unlocked and perform the correct steps
+  as necessary.
+
 ## How it works
 There are several ways the firmware can protect itself from being overwritten.
 One way is the Intel Flash Descriptor (IFD) permissions. On Intel systems, the