mx6cuboxi: Fix the reset delay for the AR8035 PHY

mx6cuboxi: Fix the reset delay for the AR8035 PHY

Since commit 59370f3fcd1350 ("net: phy: delay only if reset handler is
registered") Ethernet is no longer functional:

Booting from net ...
FEC Waiting for PHY auto negotiation to complete......... TIMEOUT !
BOOTP broadcast 1
BOOTP broadcast 2
BOOTP broadcast 3
BOOTP broadcast 4

This commit does not have an issue in itself, but it revelead a problem
with the Ethernet initialization.

As per the AR8035 datasheet:

"For a reliable power on reset, suggest to keep asserting the reset
low long enough (10ms) to ensure the clock is stable and clock-to-reset
1ms requirement is satisfied."

So do as suggested and keep the reset low for 10ms.

Also add a 100us delay after deasserting the reset line
to guarantee that the PHY ID can be read correctly and the Atheros
PHY can be loaded as per Troy Kisky's suggestion.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Tested-by: Tom Rini <trini@konsulko.com>