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
diff --git a/openpower/package/skiboot/skiboot.mk b/openpower/package/skiboot/skiboot.mk
index b14855f..74c6623 100644
--- a/openpower/package/skiboot/skiboot.mk
+++ b/openpower/package/skiboot/skiboot.mk
@@ -6,7 +6,13 @@
 
 SKIBOOT_VERSION = $(call qstrip,$(BR2_SKIBOOT_VERSION))
 
+ifeq ($(BR2_SKIBOOT_CUSTOM_GIT),y)
+SKIBOOT_SITE = $(call qstrip,$(BR2_SKIBOOT_CUSTOM_REPO_URL))
+SKIBOOT_SITE_METHOD = git
+else
 SKIBOOT_SITE = $(call github,open-power,skiboot,$(SKIBOOT_VERSION))
+endif
+
 SKIBOOT_LICENSE = Apache-2.0
 SKIBOOT_LICENSE_FILES = LICENCE
 SKIBOOT_INSTALL_IMAGES = YES