net: phy: mscc: add support for VSC8574 PHY

The VSC8574 PHY is a 4-ports PHY that is 10/100/1000BASE-T, 100BASE-FX,
1000BASE-X and triple-speed copper SFP capable, can communicate with
the MAC via SGMII, QSGMII or 1000BASE-X, supports WOL, downshifting and
can set the blinking pattern of each of its 4 LEDs, supports SyncE as
well as HP Auto-MDIX detection.

This adds support for 10/100/1000BASE-T, SGMII/QSGMII link with the MAC,
WOL, downshifting, HP Auto-MDIX detection and blinking pattern for its 4
LEDs.

The VSC8574 has also an internal Intel 8051 microcontroller whose
firmware needs to be patched when the PHY is reset. If the 8051's
firmware has the expected CRC, its patching can be skipped. The
microcontroller can be accessed from any port of the PHY, though the CRC
function can only be done through the PHY that is the base PHY of the
package (internal address 0) due to a limitation of the firmware.

The GPIO register bank is a set of registers that are common to all PHYs
in the package. So any modification in any register of this bank affects
all PHYs of the package.

If the PHYs haven't been reset before booting the Linux kernel and were
configured to use interrupts for e.g. link status updates, it is
required to clear the interrupts mask register of all PHYs before being
able to use interrupts with any PHY. The first PHY of the package that
will be init will take care of clearing all PHYs interrupts mask
registers. Thus, we need to keep track of the init sequence in the
package, if it's already been done or if it's to be done.

Most of the init sequence of a PHY of the package is common to all PHYs
in the package, thus we use the SMI broadcast feature which enables us
to propagate a write in one register of one PHY to all PHYs in the same
package.
Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>