bnxt_en: refactor ethtool firmware reset types

The case statement in bnxt_firmware_reset() dangerously mixes types.
This patch separates the application processor and whole chip resets
from the rest such that the selection is performed on a pure type.

Signed-off-by: Edwin Peer <edwin.peer@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>