mwifiex: Introduce mwifiex_probe_of() to parse common properties

Introduce function mwifiex_probe_of() to parse common properties.
Interface drivers get to decide whether or not the device tree node
was a valid one (depending on the compatible property),
Lets fill "adapter->dt_node" in mwifiex_add_card().

The function mwifiex_probe_of() is currently only a place holder with
the next patch adding content to it.

Signed-off-by: Rajat Jain <rajatja@google.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>