ARM: dts: exynos: Add support for wlan to Artik 5

On the Artik 520 module, there is a bcm4354 attached to mshc_1.  Enable
it and turn on the regulator used for it, so that both WiFi & Bluetooth
will work.

Verified to work on the Artik 520 evaluation board.

Signed-off-by: Michael Lyle <mlyle@lyle.org>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>