RISC-V: Fold all the cond-move variants together

RISC-V: Fold all the cond-move variants together

Code in `riscv_expand_conditional_move' for Ventana and Zicond targets
seems like bolted on as an afterthought rather than properly merged so
as to handle all the cases together.

Fold the existing code pieces together then (observing that for short
forward branch targets no integer comparisons need to be canonicalized),
letting T-Head targets produce branchless sequences for all the integer
comparisons rather than for equality ones only, and preparing for the
handling of floating-point comparisons here across all conditional-move
targets.

	gcc/
	* config/riscv/riscv.cc (riscv_expand_conditional_move): Unify
	conditional-move handling across all the relevant targets.

(cherry picked from commit 413ebfd660793ce16f0e6173b38ad91cd2f0cf64)