linux-postmarketos-allwinner: Upgrade to 5.12.6

I rebased all of the patches (only 2 needed some changes, the rest I just did for good measure), 0009-dts-pinephone-Add-pine64-pinephone-to-compat-list.patch was dropped since it is already in this new kernel.

The kconfig changes are just after running kconfig edit, and making no changes so that it would generate a config with any new options in 5.12, to make maintenance easier moving forward.

Also enabled CONFIG_RMNET for the next ModemManager releases in which QMAP support is added. This is needed to get mobile data working with ModemManager and QMAP.