MIPS: DSPr2: Added more bilinear fast paths (without mask)

MIPS: DSPr2: Added more bilinear fast paths (without mask)

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

lowlevel-blt-bench -b

Referent (before):
  src_8888_8888 =  L1:   8.18  L2:   7.79  M:  6.32 ( 33.51%)  HT:  5.78  VT:  5.70  R:  5.61  RT:  3.79 (  29Kops/s)
  src_8888_0565 =  L1:   6.90  L2:   7.14  M:  6.47 ( 25.75%)  HT:  5.54  VT:  5.51  R:  5.46  RT:  3.53 (  28Kops/s)
  src_0565_x888 =  L1:   3.76  L2:   3.71  M:  3.37 ( 13.41%)  HT:  3.26  VT:  3.22  R:  3.20  RT:  2.58 (  23Kops/s)
  src_0565_0565 =  L1:   3.59  L2:   3.56  M:  3.47 (  9.19%)  HT:  3.19  VT:  3.18  R:  3.16  RT:  2.46 (  22Kops/s)
 over_8888_8888 =  L1:   5.99  L2:   5.66  M:  4.95 ( 26.28%)  HT:  4.40  VT:  4.38  R:  4.31  RT:  3.02 (  26Kops/s)
  add_8888_8888 =  L1:   6.84  L2:   6.39  M:  5.48 ( 29.09%)  HT:  4.80  VT:  4.79  R:  4.70  RT:  3.20 (  27Kops/s)

Optimized:
  src_8888_8888 =  L1:  18.27  L2:  16.69  M: 12.87 ( 68.25%)  HT: 11.80  VT: 11.61  R: 10.60  RT:  7.05 (  41Kops/s)
  src_8888_0565 =  L1:  15.18  L2:  14.10  M: 11.75 ( 46.71%)  HT: 10.64  VT: 10.50  R: 10.03  RT:  7.15 (  41Kops/s)
  src_0565_x888 =  L1:  10.45  L2:   9.96  M:  9.23 ( 36.72%)  HT:  8.39  VT:  8.29  R:  8.02  RT:  5.75 (  37Kops/s)
  src_0565_0565 =  L1:   9.37  L2:   8.98  M:  8.50 ( 22.53%)  HT:  7.71  VT:  7.66  R:  7.52  RT:  5.59 (  37Kops/s)
 over_8888_8888 =  L1:  12.21  L2:  11.01  M:  8.56 ( 45.36%)  HT:  7.71  VT:  7.64  R:  7.43  RT:  5.51 (  36Kops/s)
  add_8888_8888 =  L1:  17.72  L2:  15.16  M: 10.78 ( 57.13%)  HT:  9.46  VT:  9.30  R:  9.00  RT:  6.03 (  38Kops/s)