Pack some hvmop memory structures better

Pack some hvmop memory structures better

Some of the hvmop memory structures have a shocking amount of
unnecesssary padding in them.  Elements which can have only 3 values
are given 64 bits of memory, and then aligned (so that there is
padding behind them).

This patch resizes and reorganizes in the following way, (hopefully)
without introducing any differences between the layout for 32- and
64-bit.

xen_hvm_set_mem_type:
 hvmmem_type -> 16 bits
 nr -> 32 bits (limiting us to setting 16TB at a time)

xen_hvm_set_mem_access:
 hvmmem_access -> 16 bits
 nr -> 32 bits

xen_hvm_get_mem_access:
 hvmmem_access -> 16 bits

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>