CELL: add codegen for logic op, color mask

CELL: add codegen for logic op, color mask

- rtasm_ppc_spe.c, rtasm_ppc_spe.h: added a new macro function
  "spe_load_uint" for loading and splatting unsigned integers
  in a register; it will use "ila" for values 18 bits or less,
  "ilh" for word values that are symmetric across halfwords,
  "ilhu" for values that have zeroes in their bottom halfwords,
  or "ilhu" followed by "iohl" for general 32-bit values.

  Of the 15 color masks of interest, 4 are 18 bits or less,
  2 are symmetric across halfwords, 3 are zero in the bottom
  halfword, and 6 require two instructions to load.

- cell_gen_fragment.c: added full codegen for logic op and
  color mask.