MIPS: Define & use CP0_EBase bit definitions

Add definitions for the bits & fields in the CP0_EBase register, and use
them from a few different places in arch/mips which hardcoded these
values.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Jayachandran C <jchandra@broadcom.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13222/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>