This patch adds wifi support to the ASUS Tinker Board (S) machines.

This is provided by an wifi card (RTL8723BS) wired into the sdio interface.

It requires certain pins pulled, to enable the WiFi.

The schematics for these board do not show the WiFi connection, so the
connections have been taken from:

https://github.com/TinkerBoard/debian_kernel/blob/develop/arch/arm/boot/dts/rk3288-miniarm.dts

In particular the pulling of two pins.
Co-developed-by: NStefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: NDavid Summers <beagleboard@davidjohnsummers.uk>
Signed-off-by: NStefan Wahren <stefan.wahren@i2se.com>
Tested-by: NTony McKahan <tonymckahan@gmail.com>
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>