hw/arm/stellaris: Expand comment about handling of OLED chipselect

The stellaris board doesn't emulate the handling of the OLED
chipselect line correctly.  Expand the comment describing this,
including a sketch of the theoretical correct way to do it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
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Given the stellaris board is old and not very useful these days,
I didn't think it worth the effort of actually implementing the
correct behaviour, but I wanted to record what I figured out
from various data sheets while I was looking at PL061 stuff...
1 file changed