cnss: Add optional property to control wlan_en gpio for Dual-Wifi platforms

The WIFI PCIe Clock is controlled by WLAN_EN gpio.
On Dual-WiFi Platforms, QCA WIFI SDIO chip clock sourced by PCIe Clock.

Turning off WLAN_EN gpio would result in SDIO WIFI Functional Failures.
Control the gpio, based on the platform.

CRs-Fixed: 990796
Change-Id: I1399cd8aa53d1c6fd6b8ff0c5cce66b978770dbd
Signed-off-by: Komal Seelam <kseelam@codeaurora.org>
Signed-off-by: Sarada Prasanna Garnayak <sgarna@codeaurora.org>