Allow LEDs to be blinked if the driver supports it. Enable this for
sandbox so that the tests run.

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>

We normally use -ENODEV for a missing device, rather than -ENOENT. The
latter is reserved for when we have a device but cannot find something
within it.

Also avoid looking at the root LED device since it is only a container.

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

Add a simple uclass for LEDs, so that these can be controlled by the device
tree and activated when needed. LEDs are referred to by their label.

This implementation requires a driver for each type of LED (e.g GPIO, I2C).

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