main/zfs-lts-5.15.1-r0: GPL-incompatible module zfs.ko uses GPL-only symbol 'mmu_feature_keys'

zfs-lts fails to build on ppc64le:

  MODPOST /home/buildozer/aports/main/zfs-lts/src/zfs-2.1.1/5.15.1-0-lts/module/Module.symvers
ERROR: modpost: GPL-incompatible module zfs.ko uses GPL-only symbol 'mmu_feature_keys'
make[4]: *** [scripts/Makefile.modpost:134: /home/buildozer/aports/main/zfs-lts/src/zfs-2.1.1/5.15.1-0-lts/module/Module.symvers] Error 1

See:

• https://build.alpinelinux.org/buildlogs/build-3-15-ppc64le/main/zfs-lts/zfs-lts-5.15.1-r0.log
• Upstream issue: https://github.com/openzfs/zfs/issues/11958
• Upstream issue: https://github.com/openzfs/zfs/issues/12590
• Ubuntu patch: https://git.launchpad.net/ubuntu/+source/zfs-linux/tree/debian/patches/ubuntu/4900-ppc-get-user-workaround.patch