KVM: MIPS/MMU: Invalidate GVA PTs on ASID changes

Implement invalidation of large ranges of virtual addresses from GVA
page tables in response to a guest ASID change (immediately for guest
kernel page table, lazily for guest user page table).

We iterate through a range of page tables invalidating entries and
freeing fully invalidated tables. To minimise overhead the exact ranges
invalidated depends on the flags argument to kvm_mips_flush_gva_pt(),
which also allows it to be used in future KVM_CAP_SYNC_MMU patches in
response to GPA changes, which unlike guest TLB mapping changes affects
guest KSeg0 mappings.

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