Bump skiboot to 5.1.12, to current master for garrison

Since Garrison is building from skiboot master rather than 5.1.x
stable branch during bringup, since the libgcc dependency removal
patch was merged into skiboot stable (and master) we don't need
it in op-build anymore and we need to bump garrison skiboot to
continue to build.

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/openpower/package/skiboot/Config.in b/openpower/package/skiboot/Config.in
index 5800fc0..7f42b8e 100644
--- a/openpower/package/skiboot/Config.in
+++ b/openpower/package/skiboot/Config.in
@@ -31,7 +31,7 @@
 
 config BR2_SKIBOOT_VERSION
 	string
-	default "skiboot-5.1.11" if BR2_SKIBOOT_LATEST_VERSION
+	default "skiboot-5.1.12" if BR2_SKIBOOT_LATEST_VERSION
 	default BR2_SKIBOOT_CUSTOM_VERSION_VALUE \
 		if BR2_SKIBOOT_CUSTOM_VERSION