tile: add <asm/word-at-a-time.h> and enable support functions

This change enables the generic strncpy_from_user() and strnlen_user()
using word-at-a-time.h.  The tile implementation is trivial since
both tilepro and tilegx have SIMD operations that do byte-wise
comparisons against immediate zero for each byte, and return an
0x01 byte in each position where there is a 0x00 byte.

Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>

diff --cc arch/tile/Kconfig
Simple merge

diff --cc arch/tile/include/asm/uaccess.h
Simple merge

diff --cc arch/tile/include/asm/word-at-a-time.h
Simple merge

diff --cc arch/tile/lib/exports.c
Simple merge

diff --cc arch/tile/lib/usercopy_32.S
Simple merge

diff --cc arch/tile/lib/usercopy_64.S
Simple merge