tegra: gpio: Show the GPIO value for outputs

tegra: gpio: Show the GPIO value for outputs

The tegra GPIO controller has two ways of reading the value of a GPIO. It
can supply the 'input' value (which is the value read from the pin) and the
'output' value (which is the value being driven from the pin. With a GPIO
set to output mode, the 'input' value is always low which is not very
useful.

This has the unfortunate result that setting a GPIO high still leaves it
showing as low in the 'gpio status' command.

Adjust the driver to check which direction the GPIO is set to, then read
the value from the appropriate register: 'input' for input GPIOs, 'output'
for output GPIOs.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>