MIPS: DSPr2: Added more fast-paths for REVERSE operation:

MIPS: DSPr2: Added more fast-paths for REVERSE operation:
 - out_reverse_8_0565
 - out_reverse_8_8888

Performance numbers before/after on MIPS-74kc @ 1GHz:

lowlevel-blt-bench results

Referent (before):
        out_reverse_8_0565 =  L1:  14.29  L2:  13.58  M: 12.14 ( 24.16%)  HT:  9.23  VT:  9.12  R:  8.84  RT:  4.75 (  36Kops/s)
        out_reverse_8_8888 =  L1:  27.46  L2:  23.24  M: 17.41 ( 57.73%)  HT: 12.61  VT: 12.47  R: 11.79  RT:  5.86 (  41Kops/s)

Optimized:
        out_reverse_8_0565 =  L1:  28.24  L2:  25.64  M: 20.63 ( 41.05%)  HT: 16.69  VT: 16.14  R: 15.50  RT:  8.69 (  52Kops/s)
        out_reverse_8_8888 =  L1:  52.78  L2:  41.44  M: 23.50 ( 77.94%)  HT: 18.79  VT: 18.16  R: 16.90  RT:  9.11 (  53Kops/s)