tgsi/lowering: add support for lowering FLR and CEIL

tgsi/lowering: add support for lowering FLR and CEIL

Add support for lowering FLR and CEIL to FRC/SUB and FRC/ADD
instructions for GPUs that support FRC but not FLR or CEIL.  Since
these uses FRC, it is invalid to ask for FLR or CEIL to be lowered
along with FRC, so add an assert to catch this invalid configuration.

We also need to deal with FLR instructions emitted by the lowering
code.  Fix these up with the FRC+SUB equivalent when FLR lowering is
enabled.

Signed-off-by: Russell King <rmk@arm.linux.org.uk>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Rob Clark <robclark@freedesktop.org>