After having set a new format re-calculate the pixel_rate and link_freq
control values and update them when in MIPI mode.

Take into account the limitation of the link frequency having to be
strictly smaller than 1GHz when computing the desired link_freq, and
adjust the resulting pixel_rate acounting for the clock tree
configuration.

[Adjust link_freq calculation]
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>