riscv: fix cross compiler

riscv: fix cross compiler

Move riscv_get_valid_option_values out of

Fixes:
riscv/riscv-common.cc:1748:40: error: ‘riscv_get_valid_option_values’ was not declared in this scope

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc
	  (riscv_get_valid_option_values): Get out of ifdef.