bridge: mrp: Add 'enum br_mrp_hw_support'

Add the enum br_mrp_hw_support that is used by the br_mrp_switchdev
functions to allow the SW to detect the cases where HW can't implement
the functionality or when SW is used as a backup.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>