net: remove cdns,at32ap7000-macb device tree entry

net: remove cdns,at32ap7000-macb device tree entry

The AVR32 architecture has been removed from the kernel in commit
880af7de3413264d72e5db1537a23ce2c2390b4e, hence clean out the
cdns,at32ap7000-macb compatible entry in Cadence macb Ethernet driver.

AVR32 architecture never supported device tree, hence this code was not
used by anybody.

Updated documentation to match the default entry, no users of
cdns,at32ap7000-macb in the kernel tree.

Signed-off-by: Hans-Christian Noren Egtvedt <egtvedt@samfundet.no>