net: cadence: macb: Implement BQL

Implement byte queue limits to allow queuing disciplines to account for
packets enqueued in the ring buffer but not yet transmitted. There are a
separate set of transmit functions for AT91 that I haven't touched since
I don't have hardware to test on.

Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Link: https://patch.msgid.link/20250220164257.96859-1-sean.anderson@linux.dev


Signed-off-by: Jakub Kicinski <kuba@kernel.org>