RISC-V: Use asm-generic for {in,out}{bwlq}

The asm-generic implementation is functionally identical to the RISC-V
version.

Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>