enc_neon: initialize vectors w/vdup_n_u32

replaces {} initialization gnu-ism

Change-Id: I5a7b2d4246f0205e4bfb7f4b77d720c47d8674ec
1-3% faster encoding optimizing SSE_NxN functions

got rid of the |a-b|^|b-a| method and went back
to just (a-b)^2 instead.

quality | size(bytes) after/before | time (ms) after/before

Change-Id: Ia3e0e6507b3f903deb1e182f78dad6df07380fd0
Merge "enc_neon: initialize vectors w/vdup_n_u32"