lantiq: add Linux 5.10 support as testing kernel

lantiq: add Linux 5.10 support as testing kernel

Following changes are made to the Lantiq kernel patches:

  0001-MIPS-lantiq-add-pcie-driver.patch
    The pci header isn't included by the of_pci header any longer

  0024-MIPS-lantiq-revert-DSA-switch-driver-PMU-clock-chang.patch
    Due to the merge of grx390 and ar10 clocks, extend support to grx390

  0025-NET-MIPS-lantiq-adds-xrx200-legacy.patch
    The do_carrier arguments was dropped from phy_link_change. The
    phylib has always sets the third parameter to true so the flag is
    always changed anyway.

    of_get_phy_mode() returns an error, or 0 on success, and pass a
    pointer, of type phy_interface_t, where the phy mode should be
    stored now. So far an error wasn't considered. Print at least an
    error message if something unexpected happens.

    The stuck queue is now passed to xrx200_tx_timeout (the timeout
    handler) but not used so far.

  0028-NET-lantiq-various-etop-fixes.patch
    ioremap has provided non-cached semantics by default since the Linux
    2.6 days and was removed with kernel version 5.6.

    of_get_phy_mode() returns an error, or 0 on success, and pass a
    pointer, of type phy_interface_t, where the phy mode should be
    stored now. So far an error wasn't considered. Print at least an
    error message if something unexpected happens.

  0042-arch-mips-increase-io_space_limit.patch
    Move IO space extension to laniq specific file

Signed-off-by: Mathias Kresin <dev@kresin.me>