ath25: add kernel 5.10 support

ath25: add kernel 5.10 support

Copy and refresh patches and config from 5.4 to 5.10. Most patches
require no more then automatic refresh. The only exception is the
Ethernet driver patch, which requires some more work:
* drop eth_change_mtu() usage since it was removed from the kernel,
  it anyway useless for drivers that utilizes alloc_etherdev();
* add the txqueue number argument to the .ndo_tx_timeout callback
  function;
* replace ioremap_nocache() which was finally removed from the kernel by
  the ioremap() with the same behaviour.

Switch target to the new kernel version.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
[use KERNEL_TESTING_PATCHVER for now]
Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>