net/cadence_gem: Set PHY autonegotiation restart status

net/cadence_gem: Set PHY autonegotiation restart status

The Linux kernel PHY driver sets AN_RESTART in the BMCR of the
PHY when autonegotiation is started.
Recently the kernel started to read back the PHY's AN_RESTART
bit and now checks whether the autonegotiation is complete and
the bit was cleared [1]. Otherwise the link status is down.

The emulated PHY needs to clear AN_RESTART immediately to inform
the kernel driver about the completion of autonegotiation phase.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c36757eb9dee

Signed-off-by: Linus Ziegert <linus.ziegert+qemu@holoplot.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20191104181604.21943-1-linus.ziegert+qemu@holoplot.com
Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>