kernel/power/snapshot.c: use linux/set_memory.h

kernel/power/snapshot.c: use linux/set_memory.h

This header always exists, so doesn't require an ifdef around its
inclusion.  When CONFIG_ARCH_HAS_SET_MEMORY=y it includes the asm
header, otherwise it provides empty versions of the set_memory_xx()
routines.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Michael Ellerman <[email protected]>
Acked-by: Kees Cook <[email protected]>
Acked-by: Laura Abbott <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>