RISC-V: Add missing jump label initialization

The jump_label_init() should be called from setup_arch() very
early for proper functioning of jump label support.

Fixes: ebc00dde

 ("riscv: Add jump-label implementation")
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>