consolidate asm/const.h to linux/const.h

Make a global linux/const.h header file instead of having multiple,
per-arch files, and convert current users of asm/const.h to use
linux/const.h.

Built on x86_64 and sparc64.

[akpm@linux-foundation.org: fix include/asm-x86_64/Kbuild]
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>