target/riscv: Restrict semihosting to TCG

target/riscv: Restrict semihosting to TCG

Semihosting currently uses the TCG probe_access API. To prepare for
encoding the TCG dependency in Kconfig, do not enable it unless TCG
is available.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Anton Johansson <anjo@rev.ng>
Message-Id: <20240717105723.58965-7-philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240718094523.1198645-14-alex.bennee@linaro.org>