Switch Global 2 Registers support

configname: CONFIG_NET_DSA_MV88E6XXX_GLOBAL2

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>Distributed Switch Architecture drivers
└─>Switch Global 2 Registers support
In linux kernel since version 4.1 (release Date: 2015-06-21)  
This registers set at internal SMI address 0x1C provides extended
features like EEPROM interface, trunking, cross-chip setup, etc.

It is required on most chips. If the chip you compile the support for
doesn't have such registers set, say N here. In doubt, say Y.