target/riscv: csr: Remove compile time XLEN checks

target/riscv: csr: Remove compile time XLEN checks

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>
Tested-by: Bin Meng <bin.meng@windriver.com>
Message-id: 7371180970b7db310d3a1da21d03d33499c2beb0.1608142916.git.alistair.francis@wdc.com