ARM: tegra: Implement tegra_plle_enable()

This function is required by PCIe and SATA. This patch implements it on
Tegra20, Tegra30 and Tegra124. It isn't implemented for Tegra114 because
it doesn't support PCIe or SATA.

Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>