Implement vmi_kmap_atomic_pte in terms of the backend set_linear_mapping
operation.  The conversion is rather straighforward; call kmap_atomic
and then inform the hypervisor of the page mapping.

The _flush_tlb damage is due to macros being pulled in from highmem.h.
Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andi Kleen <ak@suse.de>