mlxsw: pci: Utilize MRSR register to perform FW reset

So far, the PCI BAR0 register is used for triggering FW reset. However,
that is a legacy attitude and it is recommended to use MRSR to perform
reset instead. So do that. Move the reset into init() function as
the cmd interface needs to be used. With that, IRQ initialization needs
to be moved as well. As a side effect, the reset move simplifies
the devlink reload flow.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>