tegra: Add tegra keyboard driver

Add support for internal matrix keyboard controller for Nvidia Tegra
platforms. This driver uses the fdt decode function to obtain its key
codes.

Support for the Ctrl modifier is provided. The left and right ctrl keys are
dealt with in the same way.

This uses the new keyboard input library (drivers/input/input.c) to decode
keys and handle most of the common input logic. The new key matrix library
is also used to decode (row, column) key positions into key codes.

The intent is to make this driver purely about dealing with the hardware.

Key detection before the driver is loaded is supported. This key will be
picked up when the keyboard driver is initialized.

Modified by Bernie Thompson <bhthompson@chromium.org> and
Simon Glass <sjg@chromium.org> for device tree, input layer, key matrix
and various other things.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>