mwl8k: Fix the firmware hang issue for 8764

mwl8k: Fix the firmware hang issue for 8764

The firmware hang issue is not seen very often,
though it is still seen sometimes (once in 12
hours in local tests). The changes in the driver
,to interrupt the firmware, are needed when we
detect that firmware is stuck and when the host
queues are full and we begin to drop packets.
This is to ensure that the firmware does not
miss any PPA_RDY interrupts to cause the firmware
restart dont miss PPA_READY interrupt for SC2

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>