xen: create wrappers for all other uses of xc_hvm_XXX() functions

xen: create wrappers for all other uses of xc_hvm_XXX() functions

This patch creates inline wrapper functions in xen_common.h for all open
coded calls to xc_hvm_XXX() functions outside of xen_common.h so that use
of xen_xc can be made implicit. This again is in preparation for the move
to using libxendevicemodel.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Anthony Perard <anthony.perard@citrix.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>