Added device tree supporting code and cleaning up code following Codi…

[cat73220]

…ngStyle guide.

• driver/input/touchscreen/ft6x06_ts.c
• driver/input/touchscreen/stmpe-ts.c
• driver/power/Kconfig
• driver/power/rpi_power_switch.c
• driver/staging/fbtft/fb_hx8357d.c
• driver/staging/fbtft/fb_hx8357d.h

Added device tree overlay source file

• arch/arm/boot/dts/overlays/Makefile
• arch/arm/boot/dts/overlays/README
• arch/arm/boot/dts/overlays/rpi-power-switch-overlay.dts

Added reference build kernel configuration file for the above modification

• arch/arm/configs/masatang_defconfig

Note: using fb_hx8357d.ko and stmpe-ts.ko requires to use pitft35r-overlay.dtb. The source file of the overlay can be found at Adafruit-kernel-o-matic git repository of Adafruit account of github.com