Add documentation for the following items:

- new machines (AML M5900, VMTS, NexVision)
- updated rtc section
- removed comments about mtd cvs
- added spi section
- led section
Signed-off-by: NBen Dooks <ben-linux@fluff.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>