doc: fix runtime options in DLB2 guide

doc: fix runtime options in DLB2 guide

Convert to PCI "--allow" devarg format.
The documentation was previously using the "--vdev" form, which cannot
be used with the DLB2 PF PMD.

Fixes: f3cad285bb88 ("event/dlb2: add infos get and configure")
Fixes: f7cc194b0f7e ("event/dlb2: add enqueue and its burst variants")
Fixes: a2e4f1f5e79f ("event/dlb2: add dequeue and its burst variants")
Fixes: 95aa7101cd3c ("doc: add some features to DLB2 guide")
Cc: stable@dpdk.org
Signed-off-by: Timothy McDaniel <timothy.mcdaniel@intel.com>
Signed-off-by: David Marchand <david.marchand@redhat.com>