net: phy: move PHY package MMD access function declarations from phy.h to phylib.h

These functions are used by PHY drivers only, therefore move their
declaration to phylib.h.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/406c8a20-b62e-4ee3-b174-b566724a0876@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>