TC alpha bus_space functions

[Felix Deichmann]

Hi,

while writing "slhci at tc" support, I noticed TC bus_space functions
for alpha don't work as they should (tc_bus_mem.c). Consideration of
dense vs. sparse space seems problematic, especially for widths < 4.

I found information mainly in

[1] https://web-docs.gsi.de/~kraemer/COLLECTION/DEC/d3syspmb.pdf
[2]
http://h20565.www2.hpe.com/hpsc/doc/public/display?docId=emr_na-c04623255

and a dirty (but tested) hack based on this is attached as an example.
It would be great if someone could have a look and do a cleaner version
preferably.

Especially the end of ([2] section 12.2.2) provides a summary of which
"instruction" to use for which data width in which space, and possible
side effects (unintentional double reads/writes) in dense space...

Regards,
Felix