ARM: renesas: Enable DM_ETH_PHY and SMSC PHY driver

The board comes with SMSC LAN8710A PHY, enable matching driver.
Enable DM_ETH_PHY in the process to start using DM drivers more.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
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Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Michal Simek <michal.simek@amd.com>
Cc: Nishanth Menon <nm@ti.com>
Cc: Ramon Fried <rfried.dev@gmail.com>