Apple platforms have firmware and config files identified with multiple
dimensions. We want to be able to find the most specific firmware
available for any given platform, progressively trying more general
firmwares.

To do this, first add support for passing in multiple board_types,
which will be tried in sequence.

Since this will cause more log spam due to missing firmwares, also
switch the secondary firmware fecthes to use the _nowarn variant, which
will not log if the firmware is not found.
Signed-off-by: Hector Martin <marcan@marcan.st>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/E1oZDnd-0077aG-Dk@rmk-PC.armlinux.org.uk