net: dsa: mt7530: populate supported_interfaces and mac_capabilities

Populate the supported interfaces and MAC capabilities for mt7530,
mt7531 and mt7621 DSA switches. Filling this in will enable phylink
to pre-check the PHY interface mode against the the supported
interfaces bitmap prior to calling the validate function, and will
eventually allow us to convert to using the generic validation.

Tested-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>