prism54-firmware: change prism54/p54-firmware package versioning

There are multiple prism54/p54 firmware versions for different
drivers and devices. Therefore, assigning the package version
of all the different firmware packages on the old prism54
firmware could break if any of the p54 firmwares are updated
and we need to roll out new packages.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
[removed PKG_VERSION]
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>