ARM: refactor compiler options in config.mk

Every ARM cpu config.mk (arch/arm/cpu/{CPUDIR}/config.mk) defines:

PLATFORM_RELFLAGS += -fno-common -ffixed-r8 -msoft-float

So, this patch moves the common compiler options to arch/arm/config.mk.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/arch/arm/cpu/ixp/config.mk b/arch/arm/cpu/ixp/config.mk
index 0f12f8b..fd47c60 100644
--- a/arch/arm/cpu/ixp/config.mk
+++ b/arch/arm/cpu/ixp/config.mk
@@ -8,7 +8,7 @@
 
 BIG_ENDIAN = y
 
-PLATFORM_RELFLAGS += -fno-common -ffixed-r8 -msoft-float -mbig-endian
+PLATFORM_RELFLAGS += -mbig-endian
 
 PLATFORM_CPPFLAGS += -mbig-endian -march=armv5te -mtune=strongarm1100