phy: add the IC+ IP1001 driver

This patch adds the IC+ IP1001 (Gigabit Ethernet Transceiver) driver.
I've had to add an additional delay (2ns) to adjust RX clock phase at
GMII/ RGMII interface (according to the PHY data-sheet). This helps to
have the RGMII working on some ST platforms.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>