intel_error_decode: HEAD stuff

Show the decoded HEAD value, as well as print the calculated head offset
per ringbuffer.

This will be superceded in the next commit, but that patch is way more
complicated than this one (read: error prone), so I want this here.

Example:
ringbuffer (blitter ring) at 0x00044000; HEAD points to: 0x00044950

v2: Actually make it work for all rings.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
1 file changed