drm/vmwgfx: Only build on X86

ioremap_cache() is currently not available on some architectures.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
diff --git a/drivers/gpu/drm/vmwgfx/Kconfig b/drivers/gpu/drm/vmwgfx/Kconfig
index 67720f7..b49445d 100644
--- a/drivers/gpu/drm/vmwgfx/Kconfig
+++ b/drivers/gpu/drm/vmwgfx/Kconfig
@@ -1,6 +1,6 @@
 config DRM_VMWGFX
 	tristate "DRM driver for VMware Virtual GPU"
-	depends on DRM && PCI
+	depends on DRM && PCI && X86
 	select FB_DEFERRED_IO
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA