Use _mm_set1_epi32 instead of _mm_set_epi16, less instructions produced
by compiler. This patch also removes the duplicate define of the same
function.

Speed test results:
1. Unittest for each test cases in SSE2/AV1LbdInvTxfm2d shows 60%~80%
speedup (except those case with TX_TYPE include iidentity)
2. A brief speed test shows that with this CL, for speed1 encoder speeds up
~3% and decoder speeds up ~1.8%.
(Baseline is 18976fa5)

Change-Id: I2b0e12973fda05a21d6b6eb0f0efe11df6edfb84