buildroot

linux-firmware: allow LINUX_FIRMWARE_FILES to contain wildcards

This commit will allow the LINUX_FIRMWARE_FILES variable to contain
wildcards, which will simplify the handling of firmware that are
available in numerous revisions.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>