mwl8k: Load 8764 firmware image

This differs from legacy chips i.e.
a 8764 loads firmware image without a helper image
b Check interrupt status register for download
  complete indication.

Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>
Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>