gpio/tegra: Move Tegra gpio driver to drivers/gpio

As part of the gpio driver consolidation, this patch moves the Tegra driver
into drivers/gpio

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Colin Cross <ccross@android.com>