app/vfe-vdpa: support RPC message and handle

Support RPC message with application user
to configure VDPA.

Create RPC thread to handle RPC message from application.
Call the relation API rte_vdpa to trigger
driver configuration HW.

python file vhostmgmt as RPC example.
The following command as example:
python vhostmgmt -h
python vhostmgmt mgmtpf -h
python vhostmgmt mgmtpf -a 000:04:00.0
python vhostmgmt mgmtpf -r 000:04:00.0
python vhostmgmt mgmtpf -l
python vhostmgmt vf -p 000:04:00.3 -n 24 -q 256 -s 1024 -f 200000002 -t 2048 -m 00:11:22:33:44:55
python vhostmgmt vf -a 000:04:00.3 -v /tmp/sock1
python vhostmgmt vf -l 000:04:00.3
python vhostmgmt vf -i 000:04:00.3
python vhostmgmt vf -r 000:04:00.3
python vhostmgmt vf -h
python vhostmgmt vf -d 000:04:00.3 -o 1
python vhostmgmt vf -d 000:04:00.3 -o 4 -b 2 -e 4096 -g 4096

Signed-off-by: Li Zhang <lizh@nvidia.com>

app/meson.build

@@ -18,6 +18,7 @@ apps = [
         'test-pmd',
         'test-regex',
         'test-sad',
+        'vfe-vdpa',
 ]
 
 default_cflags = machine_args + ['-DALLOW_EXPERIMENTAL_API']