[SRU] Please bump firmware revision to 8 from jammy

[Dave Jones]

[ Impact ]

The rev 1.4 variant of the 3B+ requires an updated boot firmware, specifically one at least as recent as that in jammy-updates (version 8). This should be back-ported to focal, and preferably bionic to provide support for Core 18 booting on these devices.

[ Test Plan ]

As a closed boot firmware this will need validation on all supported Pis. For bionic, this is the 2B, 3B, 3A+, and 3B+. For focal, this is the 2B, 3B, 3A+, 3B+, and 4B. Because the package includes wifi and bluetooth firmware as well as boot firmware, the following should be verified:

* Ability to boot successfully
* Ability to reboot successfully
* Ability to shutdown successfully
* That wifi can connect successfully on relevant models (all except the 2B)
* That bluetooth can pair successfully on relevant models (all except the 2B)

[ Regression Potential ]

Fairly low; the firmware in question has been in use on all relevant models in jammy for quite some time, so the regression potential for the operation of the firmware itself is low. That said, the wifi and bluetooth firmware still interacts with the kernel, and bionic and focal have different kernel versions to jammy, hence why the operation of these components will still need (re-)verification.

If issues arise they are most likely to come from the fact that linux-firmware-raspi2 was renamed to linux-firmware-raspi in jammy which affected the diversions in the package. This means the backport isn't *entirely* straight-forward and care must be taken to ensure that all relevant files end up in their correct locations with the correct diversions.