tg3: Refactor the 2nd type of cpu pause

For completeness and consistency, add common function
tg3_pause_cpu_and_set_pc(). This is only for existing fw and not used for the
57766.

Reviewed-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>