i965: Add back strict type assertions for MAD and LRP.

i965: Add back strict type assertions for MAD and LRP.

Commit 526ffdfc033ab01cf133cb7e8290c65d12ccc9be relaxed the type
assertions in brw_alu3 to allow D/UD types (required by BFE and BFI2).
This lost us the strict type checking for MAD and LRP, which require
all four types to be float.

This patch adds a new ALU3F wrapper which checks these once again.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>