staging: fbtft: add adriver for SH1106

This patch adds support for the SH1106 OLED controller chip.

It's similar to the SSD1306, however it supports only a subset of
commands and the internal video memory has a different width.

Major differences:
- Internal video memory has a width of 132 pixels
- Only a subset of commands is supported
- Only page addressing mode is supported, no support for vertical and
  horizontal addressing
- SPI frequency limited to 2 MHz according to the datasheet

Successfully tested with a 1.3" OLED display with this chip and
SPI interface.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>