rpmsg-kdrv: rpmsg_kdrv_switch: update enum rpmsg_kdrv_ethswitch_cpsw_type

Update enum rpmsg_kdrv_ethswitch_cpsw_type to reflect recent EthFW API
changes.

This change is compatible with old and new J721E EthFW and should work
with J7200 EthFW.
Only once remote CPSW instance is supported right now:
- RPMSG_KDRV_TP_ETHSWITCH_CPSWTYPE_MAIN_CPSW
- instance 0

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Tested-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>