virtchnl2: rename enum virtchnl2_cap_rss

The "enum virtchnl2_cap_rss" will be used for negotiating flow
steering capabilities. Instead of adding a new enum, rename
virtchnl2_cap_rss to virtchnl2_flow_types. Also rename the enum's
constants.

Flow steering will use this enum in the next patches.

Reviewed-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
Signed-off-by: Ahmed Zaki <ahmed.zaki@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>