feat(tegra): implement 'pwr_domain_off_early' handler

feat(tegra): implement 'pwr_domain_off_early' handler

This patch implements the pwr_domain_off_early handler for
Tegra platforms.

Powering off the boot core on some Tegra platforms is not
allowed and the SOC specific helper functions for Tegra194,
Tegra210 and Tegra186 implement this restriction.

Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>
Change-Id: I9d06e0eee12314764adb0422e023a5bec6ed9c1e