drivers/net/airoha_eth: fix packet transmission errors

drivers/net/airoha_eth: fix packet transmission errors

The dma_map_single() function calls one of the functions
  * invalidate_dcache_range(),
  * flush_dcache_range().
Both of them expect that 'vaddr' is aligned to the ARCH_DMA_MINALIGN
boundary. Unfortunately, RX/TX descriptors are 32-byte long. Thus they
might not be aligned to the ARCH_DMA_MINALIGN boundary. Data flushing
(or invalidating) might do nothing in this case.

The same applies to dma_unmap_single() function.

In the TX path case the issue might prevent package transmission (filled
TX descriptor was not flushed).

To fix an issue a special wrappers for
  * dma_map_single(),
  * dma_unmap_single()
functions were created. The patch fix flushing/invalidatiog for the
RX path as well.

The bug appears on 32-bit airoha platform, but should be present on
64-bit as well.

The code was tested both on 32-bit and 64-bit airoha boards.

Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu>