target/riscv: add ssu64xl

target/riscv: add ssu64xl

ssu64xl is defined in RVA22 as:

"sstatus.UXL must be capable of holding the value 2 (i.e., UXLEN=64 must
be supported)."

This is always true in TCG and it's mandatory for RVA23, so claim
support for it.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250115184316.2344583-2-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>