msm_11ad: add rfclk3 clock handling

On platforms where the power supply for 11AD is external
the wil6210 device can control the rfclk3 clock using a GPIO.
wil6210 driver has to enable the clock during device reset
to guarantee the rfclk3 is on for bootloader activity.
After the wil6210 device is up, the wil6210 driver needs to
leave only the pin clock enabled, to allow the device to
toggle it.

Change-Id: I0f6181d18268f7a2f615155525fbed0f0fe7572a
CRs-Fixed: 986130
Signed-off-by: Maya Erez <merez@codeaurora.org>