ARM: dts: Reuse I2C3 for NVEC

Instead of duplicating the I2C3 node and adding NVEC specific
properties, reuse the I2C3 node, extend it with NVEC specific properties
and drop properties that are not needed by NVEC. This results in a DTB
that is a bit cleaner and avoids accidentally using I2C3 and NVEC which
would have them fight over the same hardware resources.

Signed-off-by: Thierry Reding <treding@nvidia.com>