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/lib/interrupts.c b/arch/arm/lib/interrupts.c
index 06f4679..ec3fb77 100644
--- a/arch/arm/lib/interrupts.c
+++ b/arch/arm/lib/interrupts.c
@@ -123,8 +123,8 @@
 
 void show_regs (struct pt_regs *regs)
 {
-	unsigned long flags;
-	const char *processor_modes[] = {
+	unsigned long __maybe_unused flags;
+	const char __maybe_unused *processor_modes[] = {
 	"USER_26",	"FIQ_26",	"IRQ_26",	"SVC_26",
 	"UK4_26",	"UK5_26",	"UK6_26",	"UK7_26",
 	"UK8_26",	"UK9_26",	"UK10_26",	"UK11_26",