net: phy: mscc: Add MODULE_FIRMWARE macros

The driver requires firmware so define MODULE_FIRMWARE so that modinfo
provides the details.

Fixes: fa164e40

 ("net: phy: mscc: split the driver into separate files")
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Link: https://lore.kernel.org/r/20220316151835.88765-1-juergh@canonical.com


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