Remove all spaces at end-of-line

If you find this patch with "git blame" please use "git blame -w"
to have all white-space ignored while associating lines to commits.

This commit has no practical effect but cleanup. I made it
with sed like this:

  git grep -l '[ \t]$' | xargs sed -i 's/[ \t]*$//'

However, I had to manually restore doc/wrpc_mon.png after the fact.
Similarly, I restored the include/hw/*regs.h files, as they
are (most likely) auto-generated.