Staging: hv: create hv_api.h

Merge the different include/Hv*Api.h files together into
hv_api.h as they really don't justify separate files.

No code was changed here, only moving stuff around.

Cc: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>