ARM: dts: apq8064: Add pm8921 mfd and its gpio node

This patch adds pmic gpio node to the device tree, this node is
necessary for devices like wlan to control reset gpio.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Andy Gross <agross@codeaurora.org>