dev: gcdb: display: allow overriding DSI clock rate from panel header

For certain boards it may be required to fine tune the MIPI DSI clock
rates to specific frequency in order to address any EMI considerations.
To support these cases, GCDB framework allows clock rates to be
specified as part of the panel header. Modify DSI auto PLL
implementation to use these clock rates whenever they are specified.

Change-Id: Ic21aae4b2c4d89f4e5296418d2c7857d928935a6
3 files changed