target/riscv: line up all of the registers in the info register dump

Ensure the columns for all of the register names and values line up.
No functional change, just a minor tweak to the output.

Signed-off-by: Travis Geiselbrecht <travisg@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20211009055019.545153-1-travisg@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>