net/phy: Add support for CS4315/CS4340 PHY

Add support for Cortina CS4315/CS4340 10G PHY.
- This driver loads CS43xx firmware from NOR/NAND/SPI/SD device
  to initialize Cortina PHY.
- Cortina PHY has non-standard offset of PHY ID registers, thus
  we define own get_phy_id() to override default get_phy_id().
- To define macro CONFIG_PHY_CORTINA will enable this driver.

Signed-off-by: Shengzhou Liu <Shengzhou.Liu@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>