libxc: Relocate internal-only mem_event functions to xc_private.h
The public xenctrl.h header exposes several internal-only functions of the mem_event system. As one of these functions (xc_mem_event_enable) had been previously used for a different purpose, relocating the entire set of xc_mem_event_* functions makes it easier for an external user of the library to determine which version of the mem_access system libxc exposes.
Signed-off-by: Tamas K Lengyel <tamas.k.lengyel@tum.de>
Acked-by: Ian Campbell <ian.campbell@citrix.com>