ARM: dts: dra76-evm: Add wilink8 wlan support

Add support for WLAN using wilink8 module. On dra76-evm, MMC4 is
used for connecting to wilink8 module.

Signed-off-by: Vishal Mahaveer <vishalm@ti.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>