KVM: Export include/linux/kvm.h only if $ARCH actually supports KVM

Currently, make headers_check barfs due to <asm/kvm.h>, which <linux/kvm.h>
includes, not existing.  Rather than add a zillion <asm/kvm.h>s, export kvm.h
only if the arch actually supports it.
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86/Kconfig

@@ -107,6 +107,7 @@ config ARCH_SUPPORTS_OPROFILE
 	bool
 	default y
 
+select HAVE_KVM
 
 config ZONE_DMA32
 	bool

drivers/kvm/Kconfig

 #
 # KVM configuration
 #
+config HAVE_KVM
+       bool
+
 menuconfig VIRTUALIZATION
 	bool "Virtualization"
-	depends on X86
+	depends on HAVE_KVM || X86
 	default y
 	---help---
 	  Say Y here to get to see options for using your Linux host to run other
@@ -16,7 +19,7 @@ if VIRTUALIZATION
 
 config KVM
 	tristate "Kernel-based Virtual Machine (KVM) support"
-	depends on X86 && EXPERIMENTAL
+	depends on HAVE_KVM && EXPERIMENTAL
 	select PREEMPT_NOTIFIERS
 	select ANON_INODES
 	---help---

include/linux/Kbuild

@@ -255,7 +255,7 @@ unifdef-y += kd.h
 unifdef-y += kernelcapi.h
 unifdef-y += kernel.h
 unifdef-y += keyboard.h
-unifdef-y += kvm.h
+unifdef-$(CONFIG_HAVE_KVM) += kvm.h
 unifdef-y += llc.h
 unifdef-y += loop.h
 unifdef-y += lp.h