tty: Add a new VT mode which is like VT_PROCESS but doesn't require a VT_RELDISP ioctl call

This new VT mode (VT_PROCESS_AUTO) does everything that VT_PROCESS does
except that it doesn't wait for a VT_RELDISP ioctl before switching
away from a VT with that mode.

If the X server eventually uses this new mode, debugging and crash
recovery should become easier. This is because even when currently in
the VT of a frozen X server it would still be possible to switch out
by doing SysRq-r and then CTRL-<number of a text vt>, sshing in and
doing chvt <number of a text vt>, or any other method of VT switching.
The general concensus on #xorg-devel seems to be that it should be
safe to use this with X now that we have KMS.

This also moves the VT_ACKACQ define to a more appropriate place,
for clarity's sake.

Signed-off-by: Ari Entlich <atrigent@ccs.neu.edu>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>