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
Make writes to CP0.Status and CP0.Cause have the same effect as
executing corresponding MTC0 instructions would in Kernel Mode. Also
ignore writes in the user emulation mode.
Currently for requests from the GDB stub we write all the bits across
both registers, ignoring any read-only locations, and do not synchronise
the environment to evaluate side effects. We also write these registers
in the user emulation mode even though a real kernel presents them as
read only.
Backports commit 81a423e6c6d3ccaa79de4e58024369c660c1eeb4 from qemu
Make the data type used for the CP0.Config4 and CP0.Config5 registers
and their mask signed, for consistency with the remaining 32-bit CP0
registers, like CP0.Config0, etc.
Backports commit 8280b12c0e4b515d707509dde4ddde05d9bda4ef from qemu
