riscv: Add CSR numbers

riscv: Add CSR numbers

The standard RISC-V ISA sets aside a 12-bit encoding space for up
to 4096 CSRs. This adds all known CSR numbers as defined in the
RISC-V Privileged Architecture Version 1.10.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Anup Patel <anup@brainfault.org>