CELL: changes to generate SPU code for stenciling

CELL: changes to generate SPU code for stenciling

This set of code changes are for stencil code generation
support.  Both one-sided and two-sided stenciling are supported.
In addition to the raw code generation changes, these changes had
to be made elsewhere in the system:

- Added new "register set" feature to the SPE assembly generation.
  A "register set" is a way to allocate multiple registers and free
  them all at the same time, delegating register allocation management
  to the spe_function unit.  It's quite useful in complex register
  allocation schemes (like stenciling).

- Added and improved SPE macro calculations.
  These are operations between registers and unsigned integer
  immediates.  In many cases, the calculation can be performed
  with a single instruction; the macros will generate the
  single instruction if possible, or generate a register load
  and register-to-register operation if not.  These macro
  functions are: spe_load_uint() (which has new ways to
  load a value in a single instruction), spe_and_uint(),
  spe_xor_uint(), spe_compare_equal_uint(), and spe_compare_greater_uint().

- Added facing to fragment generation.  While rendering, the rasterizer
  needs to be able to determine front- and back-facing fragments, in order
  to correctly apply two-sided stencil.  That requires these changes:
  - Added front_winding field to the cell_command_render block, so that
    the state tracker could communicate to the rasterizer what it
    considered to be the front-facing direction.
  - Added fragment facing as an input to the fragment function.
  - Calculated facing is passed during emit_quad().