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

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

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

lowlevel-blt-bench results

Referent (before):
        over_n_0565 =  L1:  14.48  L2:  21.36  M: 17.57 ( 23.30%)  HT:  6.95  VT:  6.44  R:  6.39  RT:  2.16 (  22Kops/s)
        over_n_8888 =  L1:  92.60  L2:  86.13  M: 24.41 ( 64.74%)  HT:  8.94  VT:  8.06  R:  8.00  RT:  2.53 (  25Kops/s)

Optimized:
        over_n_0565 =  L1:  27.65  L2: 189.22  M: 58.19 ( 77.12%)  HT: 52.80  VT: 49.88  R: 47.53  RT: 23.67 (  72Kops/s)
        over_n_8888 =  L1: 235.99  L2: 230.86  M: 29.09 ( 77.11%)  HT: 27.95  VT: 27.24  R: 26.58  RT: 18.10 (  67Kops/s)