RISC-V: Shorten memrefs improvement, partial fix 97417.

RISC-V: Shorten memrefs improvement, partial fix 97417.

We already have a check for riscv_shorten_memrefs in riscv_address_cost.
This adds the same check to riscv_rtx_costs.  Making this work also
requires a change to riscv_compressed_lw_address_p to work before reload
by checking the offset and assuming any pseudo reg is OK.  Testing shows
that this consistently gives small code size reductions.

	gcc/
	PR target/97417
	* config/riscv/riscv.c (riscv_compressed_lw_address_p): Drop early
	exit when !reload_completed.  Only perform check for compressed reg
	if reload_completed.
	(riscv_rtx_costs): In MEM case, when optimizing	for size and
	shorten memrefs, if not compressible, then increase cost.