target/mips: Check CPU endianness at runtime using env_is_bigendian()

target/mips: Check CPU endianness at runtime using env_is_bigendian()

Since CPU endianness can be toggled at runtime before resetting,
checking the endianness at build time preprocessing the
TARGET_BIG_ENDIAN definition isn't correct. We have to call
mips_env_is_bigendian() to get the CPU endianness at runtime.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250417131004.47205-4-philmd@linaro.org>