[ARM] 4071/1: S3C24XX: Documentation update

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: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>