Merge branch 'mv88e6xxx-isolate-Global2'

Merge branch 'mv88e6xxx-isolate-Global2'

Vivien Didelot says:

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net: dsa: mv88e6xxx: isolate Global2 support

Registers of Marvell chips are organized in internal SMI devices.

One of them at address 0x1C is called Global2. It provides an extended
set of registers, used for interrupt control, EEPROM access, indirect
PHY access (to bypass the PHY Polling Unit) and cross-chip setup.

Most chips have it, but some others don't (older ones such as 6060).

Now that its related code is isolated in mv88e6xxx_g2_* functions, move
it to its own global2.c file, making most of its setup code static.

Then make its compilation optional, which allows to reduce the size of
the mv88e6xxx driver for devices such as home routers embedding Ethernet
chips without Global2 support.

It is present on most recent chips, thus enable its support by default.

Changes in v2: fail probe if GLOBAL2 is required but not enabled.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>