RISC-V: Fix bootstrap failure.

RISC-V: Fix bootstrap failure.

	gcc/
	PR bootstrap/84856
	* config/riscv/riscv.c (riscv_function_arg_boundary): Use
	PREFERRED_STACK_BOUNDARY instead of STACK_BOUNDARY.
	(riscv_first_stack_step): Likewise.
	(riscv_option_override): Use STACK_BOUNDARY instead of
	MIN_STACK_BOUNDARY.
	* config/riscv/riscv.h (STACK_BOUNDARY): Renamed from
	MIN_STACK_BOUNDARY.
	(BIGGEST_ALIGNMENT): Set to 128.
	(PREFERRED_STACK_BOUNDARY): Renamed from STACK_BOUNDARY.
	(RISCV_STACK_ALIGN): Use PREFERRED_STACK_BOUNDARY instead of
	STACK_BOUNDARY.

From-SVN: r258650