ARM: dts: am437x: cm-t43: add dual emac support

ARM: dts: am437x: cm-t43: add dual emac support

CM-T43 comes with 2 ethernet ports connected to the cpsw subsystem, which
has 2 modes of operation: switch mode and dual emac mode.
Add the relevant muxing and set it up to work in dual emac mode by
default.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Acked-by: Mugunthan V N <mugunthanvnm@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Benoit Cousson <bcousson@baylibre.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Dmitry Lifshitz <lifshitz@compulab.co.il>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>