[media] smiapp-pll: Unify OP and VT PLL structs

Uniform representation for VT and OP clocks. This is preparation for
calculating the VT clocks using the OP clock code.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>