net: renesas: rswitch: Use hardware pause features

Since this driver used the "global rate limiter" feature of GWCA,
the TX performance of each port was reduced when multiple ports
transmitted frames simultaneously. To improve performance, remove
the use of the "global rate limiter" feature and use "hardware pause"
features of the following:
 - "per priority pause" of GWCA
 - "global pause" of COMA

Note that these features are not related to the ethernet PAUSE frame.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>