Also add sse2 versions for both.
put_pixels_clamped port and sse2 version originally written by Timothy Gu.
Reviewed-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: James Almer <jamrial@gmail.com>

This fixes cases where the scantable permuation would get overwritten by
the general idctdsp initialization.

The Xvid IDCT is only required to decode some Xvid-encoded MPEG-4 files,
so there is no point in having it as an unconditional part of idctdsp.

Also rename the enum values to be consistent with other DCT permutations.