target/mips: Have check_msa_access() return a boolean

target/mips: Have check_msa_access() return a boolean

Have check_msa_access() return a boolean value so we can
return early if MSA is not enabled (the instruction got
decoded properly, but we raised an exception).

Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20211028210843.2120802-6-f4bug@amsat.org>