ARM: 8876/1: fix O= building with CONFIG_FPE_FASTFPE

To use Fastfpe, a user is supposed to enable CONFIG_FPE_FASTFPE
and put downstream source files into arch/arm/fastfpe/.

It is not working for O= build because $(wildcard arch/arm/fastfpe)
checks if it exists in $(objtree), not in $(srctree).

Add the $(srctree)/ prefix to fix it.

While I was here, I slightly refactored the code.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/Makefile

@@ -270,14 +270,9 @@ endif
 
 export	TEXT_OFFSET GZFLAGS MMUEXT
 
-# Do we have FASTFPE?
-FASTFPE		:=arch/arm/fastfpe
-ifeq ($(FASTFPE),$(wildcard $(FASTFPE)))
-FASTFPE_OBJ	:=$(FASTFPE)/
-endif
-
 core-$(CONFIG_FPE_NWFPE)	+= arch/arm/nwfpe/
-core-$(CONFIG_FPE_FASTFPE)	+= $(FASTFPE_OBJ)
+# Put arch/arm/fastfpe/ to use this.
+core-$(CONFIG_FPE_FASTFPE)	+= $(patsubst $(srctree)/%,%,$(wildcard $(srctree)/arch/arm/fastfpe/))
 core-$(CONFIG_VFP)		+= arch/arm/vfp/
 core-$(CONFIG_XEN)		+= arch/arm/xen/
 core-$(CONFIG_KVM_ARM_HOST) 	+= arch/arm/kvm/