ARM: ux500: add DB serial number to entropy pool

This throws the DB (digital baseband, ASIC) serial number, process
type etc into the entropy pool by way of the device_add_randomness()
call. This should make every device have a unique pool state upon
boot.

Cc: Theodore Tso <tytso@mit.edu>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>