net: phy: realtek: Add support for RTL8221B-CG series

Realtek single-port 2.5Gbps Ethernet PHYs are list as below:
RTL8226-CG: the 1st generation 2.5Gbps single port PHY
RTL8226B-CG/RTL8221B-CG: the 2nd generation 2.5Gbps single port PHY
RTL8221B-VB-CG: the 3rd generation 2.5Gbps single port PHY
RTL8221B-VM-CG: the 2.5Gbps single port PHY with MACsec feature

This patch adds the minimal drivers to manage these transceivers.

Signed-off-by: Willy Liu <willy.liu@realtek.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/1604281927-9874-1-git-send-email-willy.liu@realtek.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>