devtool: deploy: provide max_process to strip_execs

Use oe.utils.get_bb_number_threads to get max_process

Signed-off-by: Clay Chang <clayc@hpe.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>