Dormito/interrupt remap v2
These are the changes I made to add an SPR to the "microwatt" core. The SPR only has 1 defined bit, the least significant bit. toggling this bit should toggle bit 30 (non-IBM bit indexing) of the effective address generated for an interrupt. In plain English: setting the bit adds 0x40000000 to generated interrupt vectors, AKA it moves the table.
The problem that it being solved here is: kestrel needs it's rom code to contain a vector table, so it has to be at 0x0. However Linux also wants to be able to control the vector table, but rom code already occupies 0x0.
I have attempted to remap the kestrel address space, so that 0x0 is dram instead, however all of my attempts have resulted in unstable core behavior, so I have at least for now, abandoned that path.
Please feel free to add comments, or make notes about things. The purpose of this MR is to get feedback.