haswell: re-add mrc.bin in separate board configs

libre mrc on haswell is quite buggy for now, but works in
a limited fashion

this patch re-adds the old configs, but as _mrc for example
t440p_12mb_mrc instead of t440p_12mb

and t440p_12mb (without _mrc) still uses the libre mrc code

resources/coreboot/t440p_12mb_mrc/board.cfg

@@ -0,0 +1,8 @@
+cbtree="default"
+romtype="t440p"
+arch="x86_64"
+payload_grub="y"
+payload_grub_withseabios="y"
+payload_seabios="y"
+payload_memtest="y"
+grub_scan_disk="ahci"