CELL: finish fragment ops blending (except for unusual D3D modes)

CELL: finish fragment ops blending (except for unusual D3D modes)

- Added new "macro" functions spe_float_min() and spe_float_max()
  to rtasm_ppc_spe.{ch}.  These emit instructions that cause
  the minimum or maximum of each element in a vector of floats
  to be saved in the destination register.

- Major changes to cell_gen_fragment.c to implement all the blending
  modes (except for the mysterious D3D-based PIPE_BLENDFACTOR_SRC1_COLOR,
  PIPE_BLENDFACTOR_SRC1_ALPHA, PIPE_BLENDFACTOR_INV_SRC1_COLOR, and
  PIPE_BLENDFACTOR_INV_SRC1_ALPHA).

- Some revamping of code in cell_gen_fragment.c: use the new spe_float_min()
  and spe_float_max() functions (instead of expanding these calculations
  inline via macros); create and use an inline utility function for handling
  "optional" register allocation (for the {1,1,1,1} vector, and the
  blend color vectors) instead of expanding with macros; use the Float
  Multiply and Subtract (fnms) instruction to simplify and optimize many
  blending calculations.