i965/fs: Expose arbitrary pull constant load sizes to the IR.

i965/fs: Expose arbitrary pull constant load sizes to the IR.

Change the FS generator to ask the dataport for enough owords worth of
constants to fill the execution size of the instruction -- Which means
that the visitor now needs to set the execution size correctly for
uniform pull constant load instructions, which we were kind of
neglecting until now.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>