staging: nvec: Add missing includes and reorder them

Add the includes that are currently missing in nvec.h
and nvec.c and reorder them alphabetically.

Signed-off-by: Julian Andres Klode <jak@jak-linux.org>
Acked-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>