checkpatch: refactor 'allowed asm includes' and add memory.h

Change the check suggesting replacement of asm-includes with
linux-includes.  Exceptions to this rule are easier to extend now.  Add
memory.h because ARM has a custom one.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>