MIPS: KVM: Clean up TLB management hazards

KVM's host TLB handling routines were using tlbw hazard barrier macros
around tlb_read(). Now that hazard barrier macros exist for tlbr, update
this case to use them.

Also fix various other unnecessary hazard barriers in this code.

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