i965/fs: Handle type-V immediates in brw_reg_from_fs_reg().

i965/fs: Handle type-V immediates in brw_reg_from_fs_reg().

We use brw_imm_v() to produce type-V immediates, which generates a
brw_reg with fs_reg's .file set to HW_REG. The next commit will rid us
of HW_REGs, so we need to handle BRW_REGISTER_TYPE_V in the IMM case.

Reviewed-by: Emil Velikov <emil.velikov@collabora.co.uk>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>