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

target/arm: 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 and this
isn't the linux-user build.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220822141230.3658237-3-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>