net: ethernet: oa_tc6: implement receive path to receive rx ethernet frames

SPI rx data buffer can contain one or more receive data chunks. A receive
data chunk consists a 64 bytes receive data chunk payload followed a
4 bytes data footer at the end. The data footer contains the information
needed to determine the validity and location of the receive frame data
within the receive data chunk payload and the host can use these
information to generate ethernet frame. Initially the receive chunks
available will be updated from the buffer status register and then it
will be updated from the footer received on each spi data transfer. Tx
data valid or empty chunks equal to the number receive chunks available
will be transmitted in the MOSI to receive all the rx chunks.
Additionally the receive data footer contains the below information as
well. The received footer will be examined for the receive errors if any.
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Parthiban Veerasooran <Parthiban.Veerasooran@microchip.com>
Link: https://patch.msgid.link/20240909082514.262942-11-Parthiban.Veerasooran@microchip.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>