Shortly, the set of supported XL will not be just 32 and 64,
and representing that properly using the enumeration will be
imperative.

Two places, booting and gdb, intentionally use misa_mxl_max
to emphasize the use of the reset value of misa.mxl, and not
the current cpu state.

Reviewed-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20211020031709.359469-5-richard.henderson@linaro.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>