doc: update ice guide
doc: update ice guide

Update the description and limitation about ice PMD according to the
product release strategy.

Signed-off-by: Xiaolong Ye <c7d6fc2f7e22da80deb234d523238b510a8c0f08@intel.com>
Acked-by: Qiming Yang <6f20802c8a43e38f9b475618bd31b5b1ac8c8656@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk