net: phy: Handle reset-delay-us/reset-post-delay-us properties

These two properties are used by various DTs in place of
current reset-assert-us/reset-deassert-us , handle both .

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>