net: dsa: b53: mmap: Add syscon reference and register layout for bcm63268

net: dsa: b53: mmap: Add syscon reference and register layout for bcm63268

On bcm63xx SoCs there are registers that control the PHYs in
the GPIO controller. Allow the b53 driver to access them
by passing in the syscon through the device tree.

Add a structure to describe the ephy control register
and add register info for bcm63268.

Signed-off-by: Kyle Hendry <kylehendrydev@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20250724035300.20497-5-kylehendrydev@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>