lcd: Provide an API to access LCD parameters

Create a basic API to provide access to lcd parameters such as screen
size, and to position the cursor on the screen.

This matches up with the video API for the same purpose. Unfortunately
they are not yet combined.

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