net: pcs: xpcs: Move native device ID macro to linux/pcs/pcs-xpcs.h

One of the next commits will alter the DW XPCS driver to support setting a
custom device ID for the particular MDIO-device detected on the platform.
The generic DW XPCS ID can be used as a custom ID as well in case if the
DW XPCS-device was erroneously synthesized with no or some undefined ID.
In addition to that having all supported DW XPCS device IDs defined in a
single place will improve the code maintainability and readability.

Note while at it rename the macros to being shorter and looking alike to
the already defined NXP XPCS ID macro.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>