Documentation/arm/sa1100: Remove some obsolete documentation

The support for the following boards, among others, was removed in 2004
with commit "[ARM] Remove broken SA1100 machine support.":

- ADS Bitsy
- Brutus
- Freebird
- ADS GraphicsClient Plus
- ADS GraphicsMaster
- Höft & Wessel Webpanel
- Compaq Itsy
- nanoEngine
- Pangolin
- PLEB
- Yopy

Tifon support has been removed in 2.4.3.3.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>