wireless-regdb: add regulatory.db[.p7s] to /lib/firmware

Starting from kernel version 4.15, Linux supports loading
regulatory.db and regulatory.db.p7s files directly from /lib/firmware,
without the need of crda. If the kernel can't load those files it'll
fallback to using crda, but the direct way is preferred.

This patch copies those those files under /lib/firmware. The use of
crda shouldn't be necessary with kernels of 4.15 or later.

Signed-off-by: Christoph Engelbert <me@noctarius.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>