clk: tegra: Add support for OSC_DIV fixed clocks

Tegra30 through Tegra210 has OSC_DIV2 and OSC_DIV4 fixed clocks
from the OSC pads.

This patch adds support for these clocks.

Tested-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>