[PlatformWithOS] Reorganisation support: Raspberry Pi + Beagle Bone Black

Reorganise and factor out common code so as to support
compilation on Raspberry Pi and Beagle Bone Black

NOTE: Beagle Bone Black is still under testing, so beware!
      Only being tested on Beagle Bone Black Angstrom
      booted from micro SD card.

Signed-off-by: Christopher Hall <christopherhall.hsw@gmail.com>
[PlatformWithOS] fix for remove target

Signed-off-by: Christopher Hall <christopherhall.hsw@gmail.com>
[PlatformWithOS] document the setup of SD Card for Beagle Bone Black

How to create an SD card of Angstrom to begin debugging the EPD
driver on this system.  These are only preliminary instructions.

Signed-off-by: Christopher Hall <christopherhall.hsw@gmail.com>
factor out the SPI BPS setting

Seems like the Beagle Bone Black needs a lower value.

Signed-off-by: Christopher Hall <christopherhall.hsw@gmail.com>
Merge pull request #1 from repaper/master

sync