release: Update u-boot and firmware file for RPI2 target

The u-boot port for RPI-2 was updated to use u-boot-master, this cause
an update in u-boot version to v2017.09 and changing the filename.
The various firmware files for the RPI* are now in a common ports
sysutils/rpi-firmware as they are shared on all the RPI version.

Update the release files to copy the right files from the right location.

Reviewed by: gjb
MFC after: 3 days