vdso: Diet include/vdso.h

In commit 2f5df09d
we included asm/type.h for bool definition. This
is fine in terms of CRIU but makes cpt2 converter
to carry the whole asm/type.h, sometimes causing
error due to confilicting definitions.

So lets be simplier and include <stdbool.h> instead.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>