The existing driver is expecting the Versaclock to be pre-programmed,
and only sets the output frequency.  Unfortunately, not all devices
are pre-programmed, and the Versaclock chip has more options beyond
just the frequency.

This patch enables the following additional features:

   - Programmable voltage: 1.8V, 2.5V, or 3.3V​
   - Slew Percentage of normal: 85%, 90%, or 100%
   - Output Type: LVPECL, CMOS, HCSL, or LVDS
Signed-off-by: Adam Ford <aford173@gmail.com>
Link: https://lore.kernel.org/r/20200603154329.31579-3-aford173@gmail.comSigned-off-by: Stephen Boyd <sboyd@kernel.org>