r8169:add support for RTL8168EP

RTL8168EP is Realtek PCIe Gigabit Ethernet controller with DASH support.
It is a successor chip of RTL8168DP.

For RTL8168EP, the read/write ocp register is via eri channel type 2, so I
move ocp_xxx() related functions under rtl_eri_xxx. And use r8168dp_ocp_xxx()
for RTL8168DP ocp read/write, r8168ep_ocp_xxx() for RTL8168EP ocp read/write.

The way of checking dash enable is different with RTL8168DP. I use
r8168dp_check_dash()for RTL8168DP and r8168ep_check_dash() for RTL8168EP,
to check if dash is enabled.

The driver_start() and driver_stop() of RTL8168EP is also different with
RTL8168DP. I use rtl8168dp_driver_xxx() for RTL8168DP and
rtl8168ep_driver_xxx for RTL8168EP.

Right now, RTL8168EP phy mcu did not need firmware code patch, so I did not
add firmware code for it.
so I did not add firmware code for it.
Signed-off-by: NChun-Hao Lin <hau@realtek.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>