net/mvpp2: add to meson build

Add support for building MRVL MVPP2 PMD with meson.  To avoid cluttering
the build environment and to keep all relevant settings local to a cross
build we get MUSDK library installation path from a meson option.

Signed-off-by: Tomasz Duszynski <tdu@semihalf.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>