lib.sh: more unified config handling

replace it with logic that simply uses "." to load
files directly. for this, "vcfg" is added as a variable
in coreboot target.cfg files, referring to a directory
in config/vendor/ containing a file named pkg.cfg, and
this file then contains the same variables as the
erstwhile config/vendor/sources

config/git files are now directories, also containing
pkg.cfg files each with the same variables as before,
such as repository link and commit hash

this change results in a noticeable reduction in code
complexity within the build system.

unified reading of config files: new function setcfg()
added to lib.sh

setcfg checks if a config exists. if a 2nd argument is
passed, it is used as a return value for eval, otherwise
a string calling err is passed. setcfg output is passed
through eval, to set strings based on config; eval must
be used, so that the variables are set within the same
scope, otherwise they'd be set within setcfg which could
lead to some whacky results.

there's still a bit more more to do, but this single change
results in a substantial reduction in code complexity.

Signed-off-by: Leah Rowe <leah@libreboot.org>

config/vendor/hp820g2/pkg.cfg

@@ -0,0 +1,9 @@
+DL_hash="1ac05a3e4f46426eeb77f89c4aca25ed1ad64479d8fcba6a3ab63a944512bacbc5d148cc7b9c4ff4b8c90a1fb1de4776e46f14aca8021900e0df37246aa0b717"
+DL_url="https://download.lenovo.com/pccbbs/mobiles/n10rg50w.exe"
+DL_url_bkup="https://download.lenovo.com/pccbbs/mobiles/n10rg50w.exe"
+MRC_url="https://dl.google.com/dl/edgedl/chromeos/recovery/chromeos_13904.77.0_samus_recovery_stable-channel_mp-v3.bin.zip"
+MRC_url_bkup="https://web.archive.org/web/20220310155922/https://dl.google.com/dl/edgedl/chromeos/recovery/chromeos_13904.77.0_samus_recovery_stable-channel_mp-v3.bin.zip"
+MRC_hash="3ff1599c52539f0707a07a8664a84ce51cd3fed1569df4bb7aa6722fc8dec0af1754250333b6ca1a9794d970a4de7b29a5cf2499f5b61e4c3eab64d1314aaea9"
+MRC_board="samus"
+MRC_refcode_cbtree="coreboot413"
+MRC_refcode_gbe="131253"