target/mips: Introduce ase_3d_available() helper

target/mips: Introduce ase_3d_available() helper

Determine if the MIPS-3D ASE is implemented by checking
the state of the 3D bit in the FIR CP1 control register.
Remove the then unused ASE_MIPS3D definition.

Note, this allows using MIPS-3D on the mips64dspr2 model.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20241021145832.34920-1-philmd@linaro.org>