net: hibmcge: support scenario without PHY

Currently, the driver uses phylib to operate PHY by default.

On some boards, the PHY device is separated from the MAC device.
As a result, the hibmcge driver cannot operate the PHY device.

In this patch, the driver determines whether a PHY is available
based on register configuration. If no PHY is available,
the driver will use fixed_phy to register fake phydev.

Signed-off-by: Jijie Shao <shaojijie@huawei.com>
Reviewed-by: Larysa Zaremba <larysa.zaremba@intel.com>
Link: https://patch.msgid.link/20250702125716.2875169-2-shaojijie@huawei.com


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