Add support for toggling an LED into the uclass interface. This can be
efficiently implemented by the driver.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ziping Chen <techping.chan@gmail.com>

It is useful to be able to read the LED as well as write it. Add this to
the uclass and update the GPIO driver.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ziping Chen <techping.chan@gmail.com>

At present this is very simple, supporting only on and off. We want to
also support toggling and blinking. As a first step, change the name of
the main method and use an enum to indicate the state.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ziping Chen <techping.chan@gmail.com>

These structures are normally named with 'uc' instead of 'uclass'. Change
this one for consistency.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ziping Chen <techping.chan@gmail.com>

At present devices use a simple integer offset to record the device tree
node associated with the device. In preparation for supporting a live
device tree, which uses a node pointer instead, refactor existing code to
access this field through an inline function.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add a test to confirm that we can adjust LEDs using the led_gpio driver.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add a simple driver which allows use of LEDs attached to GPIOs. The linux
device tree binding is used.

Signed-off-by: Simon Glass <sjg@chromium.org>