cnss: Add support for managing PCIe link, 3.3V and WLAN Enable

Add support to dynamically control the PCIe link, 3.3V and the WLAN_EN
signal based on WLAN's usage. If WLAN is turned ON 3.3V is enabled,
WLAN_EN is held high and the link is brought up. When WLAN is turned OFF,
the PCIe link is shutdown, WLAN_EN and 3.3V are disabled keeping QCA6174
completely shutdown.

The CNSS platform driver registers and manages the PCI device and provides
APIs to the WLAN driver to register and unregister with it. When WLAN
driver is loaded and unloaded the PCIe link, 3.3V and WLAN_EN GPIO are
controlled accordingly. The PCI suspend/resume calls are piggy backed
to the WLAN driver's callbacks.

When WLAN is ON, during suspend/resume the WLAN driver should take
care of saving and restoring the config space. When WLAN is OFF the
platform driver will save the config space locally and restore it
later when WLAN is switched ON the next time after PCIe link is
brought up, ensuring that the config space is restored properly.

CRs-Fixed: 571547
Change-Id: I094802383bbe4ceee3bbb0224c6d90b7401c5e3f
Acked-by: Sundar Subramaniyan <subrams@qti.qualcomm.com>
Signed-off-by: Sameer Thalappil <sameert@codeaurora.org>