dt-bindings: net: add bindings for NETC blocks control

Add bindings for NXP NETC blocks control. Usually, NETC has 2 blocks of
64KB registers, integrated endpoint register block (IERB) and privileged
register block (PRB). IERB is used for pre-boot initialization for all
NETC devices, such as ENETC, Timer, EMDIO and so on. And PRB controls
global reset and global error handling for NETC. Moreover, for the i.MX
platform, there is also a NETCMIX block for link configuration, such as
MII protocol, PCS protocol, etc.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>