drm, kdb, kms: Add an enter argument to mode_set_base_atomic() API

Some devices such as the radeon chips receive information from user
space which needs to be saved when executing an atomic mode set
operation, else the user space would have to be queried again for the
information.

This patch extends the mode_set_base_atomic() call to pass an argument
to indicate if this is an entry or an exit from an atomic kernel mode
set change.  Individual drm drivers can properly save and restore
state accordingly.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
CC: Jesse Barnes <jbarnes@virtuousgeek.org>
CC: David Airlie <airlied@linux.ie>
CC: dri-devel@lists.freedesktop.org
Signed-off-by: Dave Airlie <airlied@redhat.com>