media: mt9m114: Bypass PLL if required

media: mt9m114: Bypass PLL if required

The MT9M114 sensor has an internal PLL that generates the required SYSCLK
from EXTCLK. It also has the option to bypass the PLL and use EXTCLK
directly as SYSCLK.
The current driver implementation uses a hardcoded PLL configuration that
requires a specific EXTCLK frequency. Depending on the available clocks,
it can be desirable to use a different PLL configuration or to bypass it.

The link-frequency of the output bus (Parallel or MIPI-CSI) is configured
in the device tree.

Check if EXTCLK can be used as SYSCLK to achieve this link-frequency. If
yes, bypass the PLL.
Otherwise, (as before) check if EXTCLK and the default PLL configuration
provide the required SYSCLK to achieve the link-frequency. If yes, use the
PLL. If no, throw an error.

Signed-off-by: Mathis Foerst <mathis.foerst@mt.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>