wil6210: fix random failure to bring network interface up

Currently when we want to bring the interface up, we first
reset the device which causes the boot loader to run. Then
we halt the device CPU, load FW image and resume the device
CPU.
There are some boot loader versions which perform redundant
memory accesses even when idle. Halting the device CPU
while boot loader access memory can cause the device memory
controller to get stuck, the FW will fail to load and the
network interface will not come up.
For such boot loaders implement a workaround where we freeze
the boot loader before halting the device CPU, so it will not
perform any memory accesses.

Signed-off-by: Lior David <liord@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>