[PATCH] freepgt: remove FIRST_USER_ADDRESS hack

Once all the MMU architectures define FIRST_USER_ADDRESS, remove hack from
mmap.c which derived it from FIRST_USER_PGD_NR.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>