octeontx2-af: cn10k: Do not enable RPM loopback for LPC interfaces

octeontx2-af: cn10k: Do not enable RPM loopback for LPC interfaces

BugLink: https://bugs.launchpad.net/bugs/1959879
[ Upstream commit df66b6ebc5dcf7253e35a640b9ec4add54195c25 ]

Internal looback is not supported to low rate LPCS interface like
SGMII/QSGMII. Hence don't allow to enable for such interfaces.

Fixes: 3ad3f8f93c81 ("octeontx2-af: cn10k: MAC internal loopback support")
Signed-off-by: Geetha sowjanya <gakula@marvell.com>
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>