Depending on kernel and bootloader configuration, it's possible that
Realtek ethernet PHY isn't powered on properly. According to the
datasheet, it needs 30ms to power up and then some more time before it
can be used.

Fix that by adding 100ms ramp delay to regulator responsible for
powering PHY.

Fixes: 94dcfdc7 ("arm64: allwinner: pine64-plus: Enable dwmac-sun8i")
Suggested-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <mripard@kernel.org>