clk: tegra: pll: Add logic for out-of-table rates for T210

For Tegra210, the logic to calculate out-of-table rates is different
from previous generations. Add callbacks that can be overridden to
allow for different ways of calculating rates. Default to
_cal_rate when not specified.

This patch also includes a new flag which is used to set which method
of fixed_mdiv calculation is used. The new method for calculating the
fixed divider value for M can be more accurate especially when
fractional dividers are in play. This allows for older chipsets to use
the existing logic and new generations to use a newer version which
may work better for them.

Based on original work by Aleksandr Frid <afrid@nvidia.com>

Reviewed-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>