target/m68k: Honour -semihosting-config userspace=on

target/m68k: Honour -semihosting-config userspace=on

Honour the commandline -semihosting-config userspace=on option,
instead of never permitting userspace semihosting calls in system
emulation mode, by passing the correct value to the is_userspace
argument of semihosting_enabled(), instead of manually checking and
always forbidding semihosting if the guest is in userspace.

(Note that target/m68k doesn't support semihosting at all
in the linux-user build.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220822141230.3658237-4-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>