semihosting: Create qemu_semihosting_guestfd_init

For arm-compat, initialize console_{in,out}_gf;
otherwise, initialize stdio file descriptors.

This will go some way to cleaning up arm-compat, and
will allow other semihosting to use normal stdio.

Reviewed-by: Luc Michel <lmichel@kalray.eu>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

semihosting/console.c

@@ -190,4 +190,6 @@ void qemu_semihosting_console_init(Chardev *chr)
                                  NULL, NULL, &console,
                                  NULL, true);
     }
+
+    qemu_semihosting_guestfd_init();
 }