x86: vpx/h264/hevc/mpeg2: share constants

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
x86: better share ff_pw_2

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
x86: dwt: better share constants

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
x86: diracdsp: reuse constants

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
x86: sbrdsp/fft: reuse ps_neg constant

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