arm64: zynqmp: Remove comment about gem spec in kv260

The latest SOM specification doesn't enforce certain MIO lines allocated
for ethernet or ethernet controller itself. That's why remove comment about
it which is likely there from early version of specification.
Also removed the same comment from pinctrl node. It is clear that it has to
be defined for different carrier cards.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/9406377bf2c391ac0200670511bd6b0edb097c96.1676880543.git.michal.simek@amd.com