target/riscv: Introduce mo_endian_env() helper

target/riscv: Introduce mo_endian_env() helper

mo_endian_env() returns the target endianness from CPUArchState.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20251010155045.78220-14-philmd@linaro.org>
[ Changes by AF:
 - Only define mo_endian_env() for softmmu
]
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>