x86: convert bigmem to Kconfig

Convert the bigmem build option to Kconfig.

Signed-off-by: Doug Goldstein <cardoe@cardoe.com>

xen/arch/x86/Kconfig

@@ -25,6 +25,17 @@ config ARCH_DEFCONFIG
 
 menu "Architecture Features"
 
+config BIGMEM
+	bool "big memory support"
+	default n
+	---help---
+	  Allows Xen to support up to 123Tb of memory.
+
+	  This requires enlarging struct page_info as well as shrinking
+	  the always accessible direct mapped memory range.
+
+	  If unsure, say N.
+
 endmenu
 
 source "common/Kconfig"

xen/arch/x86/Rules.mk

@@ -23,7 +23,6 @@ $(call as-insn-check,CFLAGS,CC,".equ \"x\"$$(comma)1", \
                      '-D__OBJECT_LABEL__=$(subst $(BASEDIR)/,,$(CURDIR))/$$@')
 
 shadow-paging ?= y
-bigmem        ?= n
 
 CFLAGS += -mno-red-zone -mno-sse -fpic
 CFLAGS += -fno-asynchronous-unwind-tables
@@ -33,4 +32,3 @@ CFLAGS += -DGCC_HAS_VISIBILITY_ATTRIBUTE
 endif
 
 CFLAGS-$(shadow-paging) += -DCONFIG_SHADOW_PAGING
-CFLAGS-$(bigmem)        += -DCONFIG_BIGMEM