net: broadcom: Drop OF dependency from BGMAC_PLATFORM

All of the OF code that is used has stubbed and will compile and link
just fine, keeping COMPILE_TEST is enough.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20210106191546.1358324-1-f.fainelli@gmail.com


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