bspi problems

i got this to work using peters suggestions. though i need to polish the refactor a bit more.

im still confused about the register addresses for the channel descriptors, seems like i have to use 0x5600 for all bspi 0 descriptors, 0x5604 for all bspi descriptors and so on, whereas i would have expected 0x5600, 0x5640 like regmap indicates, but at the moment things are working and readings aren't jumping between sensors anymore. i need to finish fabbing my control board before i can really test it with many spi devices.

currently tracking my work at
github.com/sleepybishop/linuxcnc/commits...mesa-hostmot2/bspi.c
ill cherry pick changes from here to a separate branch after i clean things up (and if theres interest for my changes) to submit another pr.

anyhow just wanted to say thanks @pcw and @andypugh