cbfs: Make cbfs_master_header_props() externally available

This patch makes the CBFS default locator .locate() callback externally
available so that code which overrides cbfs_master_header_locator can
reuse or wrap it and doesn't have to copy&paste the whole thing. Use it
for the Eltan vendorcode implementation which previously did this.

Change-Id: I54dad5c8ea64ea0fc472217e275daa815736991e
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36797
Reviewed-by: Wim Vervoorn <wvervoorn@eltan.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/lib/cbfs.c

@@ -298,7 +298,7 @@ out:
 }
 
 /* This only supports the "COREBOOT" fmap region. */
-static int cbfs_master_header_props(struct cbfs_props *props)
+int cbfs_master_header_props(struct cbfs_props *props)
 {
 	struct cbfs_header header;
 	const struct region_device *bdev;