dts: Add DTS to support 1.8" TFT ST7735R

Device-Tree source describes connecting of a 1.8" (128x160) TFT display based on Sitronix ST7735R.
Lines:
	- SPI1 - SPI interface (P9 header: pins 28, 30, 31). MISO line (pin 29) is not used.
	- GPIO3 19 - DC line (P9 header: pin 27)
	- GPIO3 21 - Reset line (P9 header: pin 25)

There is no GPIO for LED cause used display has hard connection of "+" LED pin to power line.

Used display: http://www.raspberrypirobot.com/product/raspberry-pi-tft-1-8-lcd-128x160-expansion-display-board-monitor/
Used fbtft driver: https://github.com/notro/fbtft