target/mips: Make check_cp0_enabled() return a boolean

target/mips: Make check_cp0_enabled() return a boolean

To avoid callers to emit dead code if check_cp0_enabled()
raise an exception, let it return a boolean value, whether
CP0 is enabled or not.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210420193453.1913810-4-f4bug@amsat.org>