net: macb: drop usrio pointer on EyeQ5 config

net: macb: drop usrio pointer on EyeQ5 config

USRIO is disabled on this platform, drop its inherited usrio config.
We will end up with MACB_CAPS_USRIO_DISABLED on this platform:
 - We have no config->usrio so macb_configure_caps() deduces that the
   feature is disabled.
 - Anecdotally, we would also land in the runtime detection codepath
   that reads DCFG1.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20260325-stillness-undertake-d83054057b8d@spud
Signed-off-by: Jakub Kicinski <kuba@kernel.org>