x86/asm: Trim clear_page.S includes

After alternatives were shifted to the call site, only 2 headers are
necessary.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180113190648.GB23111@avx2Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/lib/clear_page_64.S

 #include <linux/linkage.h>
-#include <asm/cpufeatures.h>
-#include <asm/alternative-asm.h>
 #include <asm/export.h>
 
 /*