media: ccs-pll: Separate VT divisor limit calculation from the rest

Separate VT divisor limit calculation from the rest of the VT PLL branch
calculation. This way it can be used for dual PLL support as well.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>