net: tn40xx: add basic Rx handling

net: tn40xx: add basic Rx handling

This patch adds basic Rx handling. The Rx logic uses three major data
structures; two ring buffers with NIC and one database. One ring
buffer is used to send information to NIC about memory to be stored
packets to be received. The other is used to get information from NIC
about received packets. The database is used to keep the information
about DMA mapping. After a packet arrived, the db is used to pass the
packet to the network stack.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Hans-Frieder Vogt <hfdevel@gmx.net>
Link: https://patch.msgid.link/20240623235507.108147-6-fujita.tomonori@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>