i965/blorp/gen7+: Stop trashing push constant allocation

i965/blorp/gen7+: Stop trashing push constant allocation

Packet 3DSTATE_CONSTANT_PS is still emitted explicitly as ps stage
itself is enabled and hardware may try to prefetch constants from
the buffer. From the BSpec: 3D Pipeline - Windower -
3DSTATE_PUSH_CONSTANT_ALLOC_PS

  "Specifies the size of the PS constant buffer. This value will
   determine the amount of data the command stream can pre-fetch
   before the buffer is full."

This is not possible on gen6. From the BSpec about 3DSTATE_CONSTANT_PS:

"This packet must be followed by WM_STATE."

Binding table emissions for stages other than PS can be now dropped,
they were only needed for the 3DSTATE_CONSTANT_XS to be effective:

From the BSpec:

  "The 3DSTATE_CONSTANT_* command is not committed to the shader unit
   until the corresponding (same shader) 3DSTATE_BINDING_TABLE_POINTER_*
   command is parsed."

Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>