grub.cfg: handle extlinux in the default menuentry

isolinux/syslinux/extlinux config files should all work,
using the syslinux parser function in grub

the current behaviour is to only search for grub.cfg,
so extlinux users can't use the default libreboot setup.
with this change, their systems should hopefully work.

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

config/grub/config/grub.cfg

@@ -92,13 +92,21 @@ function search_isolinux {
 	done
 	echo # Insert newline
 }
+function try_bootcfg {
+	try_user_config "${1}"
+	try_isolinux_config "${1}"
+}
+function search_bootcfg {
+	search_grub "${1}"
+	search_isolinux "${1}"
+}
 menuentry 'Load Operating System (incl. fully encrypted disks)  [o]' --hotkey='o' {
 
 	if [ "${grub_scan_disk}" != "ata" ]; then
-		search_grub ahci
+		search_bootcfg ahci
 	fi
 	if [ "${grub_scan_disk}" != "ahci" ]; then
-		search_grub ata
+		search_bootcfg ata
 	fi
 
 	# grub device enumeration is very slow, so checks are hardcoded
@@ -113,7 +121,7 @@ menuentry 'Load Operating System (incl. fully encrypted disks)  [o]' --hotkey='o
 	# TODO: optimize grub itself, and use */? here for everything
 
 	for vol in ${lvmvol} ${raidvol} ; do
-		try_user_config "${vol}"
+		try_bootcfg "${vol}"
 	done
 
 	unset ahcidev
@@ -139,13 +147,13 @@ menuentry 'Load Operating System (incl. fully encrypted disks)  [o]' --hotkey='o
 
 	# after cryptomount, lvm volumes might be available
 	for vol in ${lvmvol}; do
-		try_user_config "${vol}"
+		try_bootcfg "${vol}"
 	done
 
-	search_grub crypto
+	search_bootcfg crypto
 
 	for vol in lvm/* ; do
-		try_user_config "${vol}"
+		try_bootcfg "${vol}"
 	done
 
 	true # Prevent pager requiring to accept each line instead of whole screen