Make the swap code conditional on CONFIG_SWAP.  This is mostly for
uClinux, but !CONFIG_SWAP compiles and boots fine for i386, too -
the only problem I've seen is that X doesn't starts, it's probably
shm-related, thus it's disabled unconditionally for "normal" arches.

The patch makes three files in mm/ conditional on CONFIG_SWAP, reorganzies
include/linux/swap.h big time to provide stubs for the !CONFIG_SWAP case,
moves the remaining /proc/swaps code to swapfile.c and cleans up some
more MM code to compile fine without CONFIG_SWAP