tty: hvc_xen: hide xen_console_remove when unused

tty: hvc_xen: hide xen_console_remove when unused

[ Upstream commit e36ae3439936e13c33f5841c7c2c1a9875acbb6d ]

xencons_disconnect_backend() is only called from xen_console_remove(),
which is conditionally compiled, so we get a harmless warning when
CONFIG_HVC_XEN_FRONTEND is unset:

hvc/hvc_xen.c:350:12: error: 'xen_console_remove' defined but not used [-Werror=unused-function]

This moves the function down into the same #ifdef section to silence
the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>