platform/target: Implement weak functions for boot device apis

Boot device related apis are used only on targets starting apq8084, msm8994
etc. We implement weak functions to enable successful compilation for
targets which doesnt use this function.

CRs-Fixed: 612217
Change-Id: I84f1a28c511cecceb0f7b8914798a3b136cb57b4
diff --git a/platform/init.c b/platform/init.c
index 1e39cfc..412184e 100644
--- a/platform/init.c
+++ b/platform/init.c
@@ -119,3 +119,13 @@
 {
 	return (uint32_t)MSM_SHARED_BASE;
 }
+
+__WEAK uint32_t platform_boot_dev_isemmc()
+{
+        return 1;
+}
+
+__WEAK uint32_t platform_get_boot_dev()
+{
+        return 0;
+}