Staging: hv: hv_mouse: reorder functions to remove forward declarations

This removes almost all forward declarations and makes all functions
static, as there should not be any global functions in this module at
all.

Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>