also update list of files expected to be seen in generated-src

PLIC: Add maxPri as well as ndev in DTS

Rename offchip-interrupts to external-interrupts.

BootROM parameters currently control the boot rom address, size, and the
hang which essentially sets the reset vector. This commit allows specifying
different parameter values as required.

I used the singular because there is really only one max priority

In particular, it is ok if no slaves actually need FIFO fixing.
It is also ok if none of those fixed are FIFO.

Fifo fixer configable

regfield: More explanatory requires so I don't have to RTFC and figure out what width actually was (#855)

Use chisel3 Clock() method.

SRAM errors

* Refactors package hierarchy.

Additionally:
  - Removes legacy ground tests and configs
  - Removes legacy bus protocol implementations
  - Removes NTiles
  - Adds devices package
  - Adds more functions to util package

PLIC: (undefZero=true) Don't allow addresses to alias

While the spec is unclear what happens when you access unused registers in the PLIC, for user simplicity turn off register aliasing. If this becomes a performance/area issue we can revisit.

L1 memory system improvements

This makes single-step exceptions higher-priority than debug interrupts.

Cache the error bit in the tag array; report precisely on access.