soc/tegra: pmc: Wait for powergate state to change

Currently, the function tegra_powergate_set() simply sets the desired
powergate state but does not wait for the state to change. In most cases
we should wait for the state to change before proceeding. Currently,
there is a case for Tegra114 and Tegra124 devices where we do not wait
when starting the secondary CPU as this is not necessary. However, this
is only done at boot time and so waiting here will only have a small
impact on boot time. Therefore, update tegra_powergate_set() to wait
when setting the powergate.

By adding this feature, we can also eliminate the polling loop from
tegra30_boot_secondary().

A function has been added for checking the status of the powergate and
so update the tegra_powergate_is_powered() to use this macro as well.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>