Correct updating XContext.Region field on mmu exceptions.
If Config3.CTXTC = 0 then the R field of XContext has to be updated
with the value of bits 63..62 of the virtual address upon a TLB
exception.
Also fixed the below line which overs 80 characters.
Backports commit 60270f85cc93d2d34e45b7679c374b1d771f0eeb from qemu
Correct computation of vector offsets for EXCP_EXT_INTERRUPT.
For instance, if Cause.IV is 0 the vector offset should be 0x180.
Simplify the finding vector number logic for the Vectored Interrupts.
Backports commit da52a4dfcc4864fd2260ec4eab331f75b1f0240b from qemu
Tighten ISA level checks down to MIPS II that many of our instructions
are missing. Also make sure any 64-bit instruction enables are only
applied to 64-bit processors, that is ones that implement at least the
MIPS III ISA.
Backports commit d9224450208e0de62323b64ace91f98bc31d6e2c from qemu
