ARM: 7022/1: allow to detect conflicting zreladdrs

Boards used to specify zreladdr in their Makefile.boot with
zreladdr-y := x, so conflicting zreladdrs were silently overwritten.
This patch changes this to zreladdr-y += x, so that we end
up with multiple words in zreladdr in such a case. We can
detect this later and complain if necessary.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/mach-w90x900/Makefile.boot b/arch/arm/mach-w90x900/Makefile.boot
index a057b54..6c3d421 100644
--- a/arch/arm/mach-w90x900/Makefile.boot
+++ b/arch/arm/mach-w90x900/Makefile.boot
@@ -1,3 +1,3 @@
-zreladdr-y	:= 0x00008000
+zreladdr-y	+= 0x00008000
 params_phys-y	:= 0x00000100