mlxbf_gige: Remove two unused function declarations

Commit f92e1869

 ("Add Mellanox BlueField Gigabit Ethernet driver")
declared but never implemented these.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Asmaa Mnebhi <asmaa@nvidia.com>
Link: https://lore.kernel.org/r/20230808145249.41596-1-yuehaibing@huawei.com


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