ath6kl: Add device tree support

This patch adds support to configure AR6004 via device-tree.

Currently, only the properties needed for AR6004 SDIO device are
provided. All other properties are added once needed for other
hardware types.

Change-Id: I306398e6c80d9bc4d86a147399b088fcba92a75f
Signed-off-by: Pavan Kumar <pavan@codeaurora.org>