cnss: Expose Power Up/Down API to WLAN Functional Driver

Dynamic Mode Change Feature Request, needs to power ON
QCA Chip during system bootup to get Firmware Capabilities.
Today the implementation is only during driver load, platform driver
power up the chip and call the device driver probe and call device driver
remove and cut the chip power during driver unload.
As part of this feature request, driver needs API to power down and
power up chip after ifconfig down and before ifconfig up.

CRs-Fixed: 1009901
Change-Id: I8e964c6bb8d6d8fb6f4bfba17a6b24b97509953c
Signed-off-by: Komal Kumar <kseelam@codeaurora.org>