BugLink: http://bugs.launchpad.net/bugs/1599109

Add a helper that can be used to obtain the number of bits per pixel
corresponding to a given MIPI DSI pixel format. This is useful in
bandwidth calculations, for example.
Signed-off-by: Liu Ying <Ying.Liu@freescale.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Chris Zhong <zyw@rock-chips.com>
[treding@nvidia.com: add kerneldoc comment and commit message]
Signed-off-by: Thierry Reding <treding@nvidia.com>

(cherry picked from commit ec26d9e9)
Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>