configs: Enable GTP (GPRS Tunneling Protocol) support

[Manawyrm]

Add support for GPRS Tunneling Protocol tunnels.

This enables the Raspberry Pi kernel to be used for open-source GSM/GPRS (2G cellular network) research & testing.
I tried to use the Osmocom / osmo-ggsn 2G stack with my Raspberry Pi 5 and ran into the issue of this module missing.

[pelwell]

What is your reasoning behind not including the 32-bit platforms?

[Manawyrm]

There is none -- that's a mistake actually :)

I looked over at your closed PR https://github.com/raspberrypi/linux/pull/7416/changes, which was merged recently and saved the defconfig for those same files.
I'll go add the 32bit defconfigs as well.

[pelwell]

Ah, yes - those parts are attached by PCIe, so there is no point enabling the drivers on any of the 32-bit only Pis.

[Manawyrm]

Seems to compile fine for 32bit kernels (I can't test more right now without setting up an entire test setup) -- I added config for those as well.

I also added the missing Signed-off-by:-line into the commit description.

[pelwell]

That's great. Once the build checks have completed (just a formality, I think), this will get merged.

[Manawyrm]

Not quite -- I ran into a mismatch with the Signed-off again, with a mismatch between my legal name and nickname.
Should hopefully be fixed now, so fingers crossed for the next CI run. Sorry about the extra step!

[pelwell]

That's good of you, but we aren't precious about defconfig changes - they all get squashed into one big "Raspberry Pi defconfigs" eventually - so we waive some of the checkpatch warnings.