net/mlx: add static ibverbs linkage with meson

net/mlx: add static ibverbs linkage with meson

The libibverbs (and libmlx4/5) can be statically embedded
in the shared PMD library, or in the application with the static PMD.
It was supported with make build system in
commit 2c0dd7b69fb0 ("config: add static linkage of mlx dependency").

The same feature is enabled with meson when using pkg-config
(i.e. only if the call to dependency() is successful).
The fallback method for searching library with cc.find_library()
is not supported because the dependencies of the found library
would not be linked (no such info in .a file unlike .so).

The main difference, in meson build system, is the generated .pc file
giving arguments to link DPDK with the application.
Unfortunately the .pc file will not keep memory of the static linkage
option for libibverbs.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>