x86: split NX setup into separate file to limit unstack-protected code

Move the NX setup into a separate file so that it can be compiled
without stack-protection while leaving the rest of the mm/init code
protected.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index dd313d0..06630d2 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -1,10 +1,10 @@
 obj-y	:=  init.o init_$(BITS).o fault.o ioremap.o extable.o pageattr.o mmap.o \
-	    pat.o pgtable.o physaddr.o gup.o
+	    pat.o pgtable.o physaddr.o gup.o setup_nx.o
 
 # Make sure __phys_addr has no stackprotector
 nostackp := $(call cc-option, -fno-stack-protector)
 CFLAGS_physaddr.o		:= $(nostackp)
-CFLAGS_init.o			:= $(nostackp)
+CFLAGS_setup_nx.o		:= $(nostackp)
 
 obj-$(CONFIG_SMP)		+= tlb.o