spl, common, serial: build SPL without serial support

This patch enables building SPL without
CONFIG_SPL_SERIAL_SUPPORT support.

Signed-off-by: Heiko Schocher <hs@denx.de>
[trini: Ensure we build arch/arm/imx-common on mx28]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 6f30098..ab0e9ce 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -78,7 +78,7 @@
 libs-y += arch/arm/lib/
 
 ifeq ($(CONFIG_SPL_BUILD),y)
-ifneq (,$(CONFIG_MX23)$(CONFIG_MX35)$(filter $(SOC), mx25 mx27 mx5 mx6 mx31 mx35))
+ifneq (,$(CONFIG_MX23)$(CONFIG_MX28)$(CONFIG_MX35)$(filter $(SOC), mx25 mx27 mx5 mx6 mx31 mx35))
 libs-y += arch/arm/imx-common/
 endif
 else