x86 plat: limit x86 platform driver menu to X86

My .config contains ACER_WMI=m. On SPARC. That does not make sense.
Restrict the x86 platform driver menu to x86.
Signed-off-by: NJan Engelhardt <jengelh@medozas.de>
Signed-off-by: NMatthew Garrett <mjg@redhat.com>

drivers/platform/x86/Kconfig

@@ -5,6 +5,7 @@
 menuconfig X86_PLATFORM_DEVICES
 	bool "X86 Platform Specific Device Drivers"
 	default y
+	depends on X86
 	---help---
 	  Say Y here to get to see options for device drivers for various
 	  x86 platforms, including vendor-specific laptop extension drivers.