MIPS: Add defs & probing of UFR

Add definitions and probing of the UFR bit in Config5. This bit allows
user mode control of the FR bit (floating point register mode). It is
present if the UFRP bit is set in the floating point implementation
register.

This is a capability KVM may want to expose to guest kernels, even
though Linux is unlikely to ever use it due to the implications for
multi-threaded programs.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org