mk: prepare dependencies in shared libraries not combined

mk: prepare dependencies in shared libraries not combined

Some DPDK libraries have a dependency.
The Mellanox drivers embed this declaration in shared library case.
So the application do not need to know the dependency when linking.
But it cannot work with static libraries or the combined one.
Note that Mellanox drivers are currently not supported in a shared
combined library case.

Most of the DPDK libraries declare their dependencies to be linked
with the application in every cases, even when using drivers as
shared library plugins.
This patch improves the condition used for Mellanox drivers, so that
it can be applied to other drivers without breaking the shared
combined library case.

Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>