[media] bdisp: add debug file system

Creates 5 debugfs entries to dump the last HW request, the last HW node
(=command), the HW registers and the recent HW performance (time & fps)

Signed-off-by: Fabien Dessenne <fabien.dessenne@st.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>