ARM: dts: qs600: add pwrseq support to WLAN

Add pwrseq support to sdcc4 which would enable a proper reset of WLAN
without ugly hacks in the board support file.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Andy Gross <agross@codeaurora.org>