project: mdm9615: Add support to override linker

Some target use ld.bfd linker instead of ld, override
the specific linker from project makefile.

CRs-Fixed: 626209
Change-Id: I1002d381132f6009eba23bd9a732f696d72e16a0
diff --git a/project/mdm9615.mk b/project/mdm9615.mk
index 08a4866..5cffa5c 100644
--- a/project/mdm9615.mk
+++ b/project/mdm9615.mk
@@ -12,3 +12,5 @@
 
 #disable Thumb mode for the codesourcery/arm-2011.03 toolchain
 ENABLE_THUMB := false
+
+LD := $(TOOLCHAIN_PREFIX)ld.bfd