generic at803x: remove unneeded patches

generic at803x: remove unneeded patches

- Remove the "RGMII TX delay fixup" hack and the associated
   DT-property. It was never used in a DT-based platform and
   solved a problem which can be mitigated by using correct
   delays on the MAC side.

 - Remove the patch to enable platform-data support for the
   at803x driver. It was only used by ar71xx which does not
   (and never will) support kernel 4.19 or later.

 - Remove the SmartEEE DT-configuration patch. As explained
   previously, this patch never disabled the Atheros SmartEEE
   implementation, but rather "standard" EEE. This can be done
   on device-tree compatible platforms by adding the
   "eee-broken-1000t" or "eee-broken-100tx" properties to the PHY
   node. As all usages of the old properties are migrated, this
   patch can be removed.

Signed-off-by: David Bauer <mail@david-bauer.net>
Acked-by: Christian Lamparter <chunkeey@gmail.com>