patches/openwrt/kernel-5.15: Move qca8k mgmt fixes to backport-5.15

This ports commit
  f4d949b40485 ("generic: 5.15: backport qca8k fixup for mgmt and mdio read/write")
from upstream OpenWRT. The commit backports 5 qca8k patches to
  target/linux/generic/backport-5.15

The patches are currently backported into
  target/linux/mpc85xx/patches-5.15
by our patch
  mpc85xx: add patches from OpenWrt to improve switch

So this basically renames and moves the patches into another directory.