mk: fix driver build with installed SDK

mk: fix driver build with installed SDK

The tool pmdinfogen was called from RTE_OUTPUT/app/ which does not exist
if building a driver outside of the SDK build.
When building DPDK, RTE_SDK_BIN is RTE_OUTPUT. When building an external
driver, RTE_SDK_BIN must point to the installed DPDK directory containing
includes, libs, etc.

That's why pmdinfogen must be installed in the SDK directory and be part
of the SDK installation.

Fixes: 3d781ca32874 ("mk: do post processing on objects that register a driver")

Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>