dsputil: x86: Move ff_inv_zigzag_direct16 table init to mpegvideo

The table is MMX-specific and used nowhere else.
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  dsputil: x86: Move ff_inv_zigzag_direct16 table init to mpegvideo

If someone optimizes dct_quantize for non x86 SIMD, then this
probably needs to be reverted.

Merged-by: Michael Niedermayer <michaelni@gmx.at>
configure: put pthread_create() check back

Unbreaks freebsd, broken since f058f384a0d76bfd125f4738dceab7c890186432

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>