drm/nouveau: report how much memory userspace tried to "validate"

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
drm/nouveau: restore debugfs support

Restore majority of debugfs support (with an exception of channel info) dropped
in commit ebb945a94bba2ce8dff7b0942ff2b3f2a52a0a69 ("drm/nouveau: port all
engines to new engine module format").

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
drm/nouveau/disp: sizeof() wrong pointer

"data" is a void pointer and "args" is "data" after we have casted it to
a struct.  We care about the size of the struct here.  Btw,
sizeof(*data) is 1.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
drm/nouveau: Fix DPMS 1 on G4 Snowball, from snow white to coal black.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=40275.

Signed-off-by: Stefan de Konink <stefan@konink.de>
Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>