skiboot: Enable use of a custom repository

We already have BR2_SKIBOOT_CUSTOM_VERSION. It would be nice if we could
also specify the repository, to test op-build configs with a
developmental skiboot.

Add CUSTOM_GIT and CUSTOM_REPO_URL options (like the similarly-named
kernel options) allowing us to do

BR2_SKIBOOT_CUSTOM_VERSION=y
BR2_SKIBOOT_CUSTOM_VERSION_VALUE="sha"
BR2_SKIBOOT_CUSTOM_GIT=y
BR2_SKIBOOT_CUSTOM_REPO_URL="ssh://git@github.com/user/skiboot.git"

Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
diff --git a/openpower/package/skiboot/Config.in b/openpower/package/skiboot/Config.in
index a8c73f0..0b1b1ac 100644
--- a/openpower/package/skiboot/Config.in
+++ b/openpower/package/skiboot/Config.in
@@ -35,6 +35,13 @@
 	default BR2_SKIBOOT_CUSTOM_VERSION_VALUE \
 		if BR2_SKIBOOT_CUSTOM_VERSION
 
+config BR2_SKIBOOT_CUSTOM_GIT
+	bool "Custom git repository"
+
+config BR2_SKIBOOT_CUSTOM_REPO_URL
+	string "URL of custom repository"
+	depends on BR2_SKIBOOT_CUSTOM_GIT
+
 endif
 
 endmenu