libs/guest: move cpu policy related prototypes to xenguest.h

libs/guest: move cpu policy related prototypes to xenguest.h

Do this before adding any more stuff to xg_cpuid_x86.c.

The placement in xenctrl.h is wrong, as they are implemented by the
xenguest library. Note that xg_cpuid_x86.c needs to include
xg_private.h, and in turn also fix xg_private.h to include
xc_bitops.h. The bitops definition of BITS_PER_LONG needs to be
changed to not be an expression, so that xxhash.h can use it in a
preprocessor if directive.

As a result also modify xen-cpuid to include xenguest.h.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>