MIPS: DSPr2: Added fast-paths for OVER operation: - over_0565_n_0565 - over_0565_8_0565

MIPS: DSPr2: Added fast-paths for OVER operation: - over_0565_n_0565 - over_0565_8_0565

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

lowlevel-blt-bench results

Referent (before):
        over_0565_n_0565 =  L1:   7.56  L2:   7.24  M:  6.16 ( 16.38%)  HT:  4.01  VT:  3.84  R:  3.79  RT:  1.66 (  18Kops/s)
        over_0565_8_0565 =  L1:   7.43  L2:   7.05  M:  5.98 ( 23.85%)  HT:  5.27  VT:  5.23  R:  5.09  RT:  3.14 (  28Kops/s)

Optimized:
        over_0565_n_0565 =  L1:  15.47  L2:  14.52  M: 12.30 ( 32.65%)  HT: 10.76  VT: 10.57  R: 10.27  RT:  6.63 (  46Kops/s)
        over_0565_8_0565 =  L1:  15.47  L2:  14.61  M: 11.78 ( 46.92%)  HT: 10.00  VT:  9.84  R:  9.40  RT:  5.81 (  43Kops/s)