vt: ioctl, switch VT_IS_IN_USE and VT_BUSY to inlines

These two were macros. Switch them to static inlines, so that it's more
understandable what they are doing.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20200219073951.16151-2-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>