boards: sama5d4-ek: Move -fno-common option to previous ARCHCFLAGS/ARCHCXXFLAGS

Summary:
- Apply the same style as sabre-6quad

Impact:
- None

Testing:
- Build only

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

boards/arm/sama5/sama5d4-ek/configs/knsh/Make.defs

@@ -49,15 +49,12 @@ ifneq ($(CONFIG_DEBUG_NOOPT),y)
 endif
 
 ARCHCPUFLAGS = -mcpu=cortex-a5 -mfpu=vfpv4-d16
-ARCHCFLAGS = -fno-builtin
-ARCHCXXFLAGS = -fno-builtin -fno-exceptions -fcheck-new -fno-rtti
+ARCHCFLAGS = -fno-common -fno-builtin
+ARCHCXXFLAGS = -fno-common -fno-builtin -fno-exceptions -fcheck-new -fno-rtti
 ARCHWARNINGS = -Wall -Wstrict-prototypes -Wshadow -Wundef
 ARCHWARNINGSXX = -Wall -Wshadow -Wundef
 ARCHPICFLAGS = -fpic -msingle-pic-base -mpic-register=r10
 
-ARCHCFLAGS += -fno-common
-ARCHCXXFLAGS += -fno-common
-
 CFLAGS := $(ARCHCFLAGS) $(ARCHWARNINGS) $(ARCHOPTIMIZATION) $(ARCHCPUFLAGS) $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe
 CPICFLAGS = $(ARCHPICFLAGS) $(CFLAGS)
 CXXFLAGS := $(ARCHCXXFLAGS) $(ARCHWARNINGSXX) $(ARCHOPTIMIZATION) $(ARCHCPUFLAGS) $(ARCHXXINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe