ARM: dts: imx6qdl-sr-som-ti: indicate powering off wifi is safe

We need to indicate that powering off the TI WiFi is safe, to avoid:

wl18xx_driver wl18xx.2.auto: Unbalanced pm_runtime_enable!
wl1271_sdio mmc0:0001:2: wl12xx_sdio_power_on: failed to get_sync(-13)

which prevents the WiFi being functional.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>