gallium: Cleanup predicate and condition code TGSI tokens.

gallium: Cleanup predicate and condition code TGSI tokens.

There is little point in having a special TGSI token just to handle
predicate register updates. Remove tgsi_dst_register_ext_predicate token
and instead use a new PREDICATE register file to update predicates.
Actually, the contents of the obsolete token are being moved
to tgsi_instruction_ext_predicate, where they should be
from the very beginning.

Remove the NVIDIA-specific condition code tokens -- nobody uses them
and they can be emulated with predicates if needed.

Introduce PIPE_CAP_SM3 that indicates whether a driver supports
SM3-level instructions, and in particular predicates.

Add PIPE_CAP_MAX_PREDICATE_REGISTERS that can be used to query the driver
how many predicate registers it supports (currently it would be 1).