net: broadcom: share header defining UniMAC registers

UniMAC is integrated into multiple Broadcom's Ethernet controllers so
use a shared header file for it and avoid some code duplication.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Doug Berger <opendmb@gmail.com>
Link: https://lore.kernel.org/r/20210107180051.1542-2-zajec5@gmail.com


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