sunxi: Fix gmac not working due to cpu_eth_init no longer being called

cpu_eth_init is no longer called for dm enabled eth drivers, this
was causing the sunxi gmac eth controller to no longer work in u-boot.

This commit fixes this by calling the clock, reset and pinmux setup
function from s_init() and enabling the phy power pin (if any) from
board_init().

The enabling of phy power cannot be done from s_init because it uses dm
and dm is not ready yet at this point.

Note that the mdelay is dropped as the phy gets enabled much earlier
now, so it is no longer needed.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
Tested-by: Karsten Merker <merker@debian.org>
Tested-by: Michael Haas <haas@computerlinguist.org>