qualcommbe: enable v6.12 testing kernel

qualcommbe: enable v6.12 testing kernel

Now that patches for v6.12 are available, add the config, and enable
6.12 as a testing kernel.

Compared to v6.6 the patches to add "10gbase-r", "2500base-x",
"1000base-x", and "10g-qxgmii" modes have not been ported yet. They do
not apply cleanly to the new PCS driver. As the currently supported
hardware does not use those modes, it is not possible to test them at
this time.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/18796
Signed-off-by: Robert Marko <robimarko@gmail.com>