doc: fix some statements for ice vector PMD

[ upstream commit c2e1296 ]

1. Add descriptions for how to select avx512 datapath.
2. Add explanation for "P" in ice.ini.

Fixes: 7f85d5e ("net/ice: add AVX512 vector path")
Fixes: 271cc8c ("doc: update ice features list")

Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>
Acked-by: Leyi Rong <leyi.rong@intel.com>

doc/guides/nics/ice.rst

@@ -211,9 +211,12 @@ are chosen based on 2 conditions.
 - ``CPU``
   On the X86 platform, the driver checks if the CPU supports AVX2.
   If it's supported, AVX2 paths will be chosen. If not, SSE is chosen.
+  If the CPU supports AVX512 and EAL argument ``--force-max-simd-bitwidth``
+  is set to 512, AVX512 paths will be chosen.
 
 - ``Offload features``
-  The supported HW offload features are described in the document ice_vec.ini.
+  The supported HW offload features are described in the document ice.ini,
+  A value "P" means the offload feature is not supported by vector path.
   If any not supported features are used, ICE vector PMD is disabled and the
   normal paths are chosen.