ARM: dts: msm: add gpio_key devices for buttons on Kona MTP, CDP and QRD

Add pinctrl configurations for home and volume up buttons which utilize
PM8150 GPIOs 1 and 6 respectively. Add gpio_key devices for these
buttons on Kona MTP, CDP and QRD targets.

Change-Id: Ia05625ddc4948130ce96e49ac20d53446c1259f4
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>