Dalmore have the keys mounted on board which are connected
to different pins of Tegra.

Add the keys entry in DTS file to enable key functionality.
This will enable KEY_POWER, KEY_HOME, KEY_VOLUMEUP and
KEY_VOLUMEDOWN.
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>