wil6210: bus_request platform operation refinement

The driver uses the bus_request platform operation to
request resources from the platform for a specific bandwidth.
Currently the driver requests resources for the maximum
theoretical bandwidth, when interface is brought up.
Refine this process a bit: now the driver will request a
small amount of resources when interface is up, and will only
issue the maximum request when connected.
This mechanism will be improved further in the future to make
more refined requests based on actual bandwidth.

Signed-off-by: Lior David <qca_liord@qca.qualcomm.com>
Signed-off-by: Maya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>