x86/platform: Fix "make O=dir kvmconfig"

x86/platform: Fix "make O=dir kvmconfig"

Running:

	make O=dir x86_64_defconfig
	make O=dir kvmconfig

the second command dirties the source tree with file ".config",
symlink "source" and objects in folder "scripts".

Fixed by using properly prefixed paths in the arch Makefile.

Signed-off-by: Antonio Borneo <[email protected]>
Acked-by: Borislav Petkov <[email protected]>
Cc: Pekka Enberg <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>