ARM: tegra: Export tegra_powergate_sequence_power_up()

This function can be used by drivers to enable power to the hardware
blocks that they drive. Most of the drivers can be built as a module
and therefore require this function to be exported.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Stephen Warren <swarren@nvidia.com>