powerpc: Update 64bit __copy_tofrom_user() using CPU_FTR_UNALIGNED_LD_STD

In exactly the same way that we updated memcpy() with new feature
sections in commit 25d6e2d7 ("powerpc:
Update 64bit memcpy() using CPU_FTR_UNALIGNED_LD_STD"), we do the same
thing here for __copy_tofrom_user().  Once again this is purely a
performance tweak for Cell and Power6 - this has no effect on all the
other 64bit powerpc chips.

We can make these same changes to __copy_tofrom_user() because the
basic copy algorithm is the same as in memcpy() - this version just
has all the exception handling logic needed when copying to or from
userspace as well as a special case for copying whole 4K pages that
are page aligned.

CPU_FTR_UNALIGNED_LD_STD CPU was added in commit
4ec577a2

 ("powerpc: Add new CPU
feature: CPU_FTR_UNALIGNED_LD_STD").

We also make the same simple one line change from cmpldi r1,... to
cmpldi cr1,... for consistency.

Signed-off-by: Mark Nelson <markn@au1.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>