x86: Use VMM API in memcmpeq-evex.S and minor changes

x86: Use VMM API in memcmpeq-evex.S and minor changes

Changes to generated code are:
    1. In a few places use `vpcmpeqb` instead of `vpcmpneq` to save a
       byte of code size.
    2. Add a branch for length <= (VEC_SIZE * 6) as opposed to doing
       the entire block of [VEC_SIZE * 4 + 1, VEC_SIZE * 8] in a
       single basic-block (the space to add the extra branch without
       changing code size is bought with the above change).

Change (2) has roughly a 20-25% speedup for sizes in [VEC_SIZE * 4 +
1, VEC_SIZE * 6] and negligible to no-cost for [VEC_SIZE * 6 + 1,
VEC_SIZE * 8]

From N=10 runs on Tigerlake:

align1,align2 ,length ,result               ,New Time ,Cur Time ,New Time / Old Time
0     ,0      ,129    ,0                    ,5.404    ,6.887    ,0.785
0     ,0      ,129    ,1                    ,5.308    ,6.826    ,0.778
0     ,0      ,129    ,18446744073709551615 ,5.359    ,6.823    ,0.785
0     ,0      ,161    ,0                    ,5.284    ,6.827    ,0.774
0     ,0      ,161    ,1                    ,5.317    ,6.745    ,0.788
0     ,0      ,161    ,18446744073709551615 ,5.406    ,6.778    ,0.798

0     ,0      ,193    ,0                    ,6.804    ,6.802    ,1.000
0     ,0      ,193    ,1                    ,6.950    ,6.754    ,1.029
0     ,0      ,193    ,18446744073709551615 ,6.792    ,6.719    ,1.011
0     ,0      ,225    ,0                    ,6.625    ,6.699    ,0.989
0     ,0      ,225    ,1                    ,6.776    ,6.735    ,1.003
0     ,0      ,225    ,18446744073709551615 ,6.758    ,6.738    ,0.992
0     ,0      ,256    ,0                    ,5.402    ,5.462    ,0.989
0     ,0      ,256    ,1                    ,5.364    ,5.483    ,0.978
0     ,0      ,256    ,18446744073709551615 ,5.341    ,5.539    ,0.964

Rewriting with VMM API allows for memcmpeq-evex to be used with
evex512 by including "x86-evex512-vecs.h" at the top.

Complete check passes on x86-64.