i965: Add fs_reg/src_reg constructors that take vf[4].

i965: Add fs_reg/src_reg constructors that take vf[4].

Sometimes it's easier to generate 4x values into an array, and the
memcpy is 1 instruction, rather than 11 to piece 4 arguments together.

I'd forgotten to remove the prototype from fs_reg from a previous patch,
so it's already there for us here.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>