PDP11: RP11: Implement original RP11 controller flavor

Studying RSX11M source code I found out that the original RP11
controller (vs. -C and -E later versions) was still supported
in the software, and notably UMD (User Mode Diagnostics) was
still capable of handing it and dealing with its testing,
even in much later OS versions (compared to when the original
RP11 was phased out).

The change in this commit basically implements that flavor
(which only supported the RP02 drives), and also makes a few
minor fixes / cleanups for the device code, here and there.

The default mode for the RP11 controller remains the more widely
used -C/-E version, but if so desired, it can be downgraded to
support its predecessor with the "SET RR <type>" command now.