octeontx2-pf: Fix linking objects into multiple modules

This patch fixes the below build warning messages that are
caused due to linking same files to multiple modules by
exporting the required symbols.

"scripts/Makefile.build:244: drivers/net/ethernet/marvell/octeontx2/nic/Makefile:
otx2_devlink.o is added to multiple modules: rvu_nicpf rvu_nicvf

scripts/Makefile.build:244: drivers/net/ethernet/marvell/octeontx2/nic/Makefile:
otx2_dcbnl.o is added to multiple modules: rvu_nicpf rvu_nicvf"

Fixes: 8e675581

 ("octeontx2-pf: PFC config support with DCBx").
Signed-off-by: Geetha sowjanya <gakula@marvell.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>