lavfi/frei0r: search plugins in lib64 dirs on all architectures

As Reimar Döffinger pointed out there are non-x86 64bit architectures as well.

Reviewed-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Marton Balint <cus@passwd.hu>
lavfi/frei0r: factorize plugin loading with static path

Reviewed-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Marton Balint <cus@passwd.hu>
Merge remote-tracking branch 'cus/stable'

* cus/stable:
  lavfi/frei0r: factorize plugin loading with static path
  lavfi/frei0r: search plugins in lib64 dirs on all architectures

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