[PATCH] x86-64: Speed and clean up cache flushing in change_page_attr

CLFLUSH is a lot faster than WBINVD so avoid the later if at all
possible.

Always pass the complete list of pages to other CPUs to cut down
the number of IPIs.

Minor other cleanup and sync with i386 version.

Signed-off-by: Andi Kleen <ak@suse.de>