coreboot: add x230edp_12mb, remove x230fhd_12mb

New x230edp_12mb target uses the
https://review.coreboot.org/c/coreboot/+/28950 patchset to add an
X230_EDP target to the default coreboot branch.
Consequently the "fhd" coreboot branch is no longer needed and has
been safely removed.

resources/coreboot/x230edp_12mb/board.cfg

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