libxl: move DEFINE_DEVICE* macros to libxl_internal.h

libxl: move DEFINE_DEVICE* macros to libxl_internal.h

In order to be able to have all functions related to a device type in
a single source file move the macros used to generate device type
specific functions to libxl_internal.h. Rename the macros as they are
no longer local to a source file. While at it hide device remove and
device destroy in one macro as those are always used in pairs. Move
usage of the macros to the appropriate source files.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>