x86emul: support MOVDIR{I,64B} insns

x86emul: support MOVDIR{I,64B} insns

Introduce a new blk() hook, paralleling the rmw() one in a certain way,
but being intended for larger data sizes, and hence its HVM intermediate
handling function doesn't fall back to splitting the operation if the
requested virtual address can't be mapped.

Note that SDM revision 071 doesn't specify exception behavior for
ModRM.mod == 0b11; assuming #UD here.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Acked-by: Andrew Cooper <andrew.cooper@citrix.com>