tcg: Move some TCG_CT_* bits to TCGArgConstraint bitfields

tcg: Move some TCG_CT_* bits to TCGArgConstraint bitfields

These are easier to set and test when they have their own fields.
Reduce the size of alias_index and sort_index to 4 bits, which is
sufficient for TCG_MAX_OP_ARGS.  This leaves only the bits indicating
constants within the ct field.

Move all initialization to allocation time, rather than init
individual fields in process_op_defs.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>