tg3: Dynamically allocate VPD data memory

This patch eases stack pressure by dynamically allocating the memory
used to temporarily store VPD data.

Reviewed-by: Benjamin Li <benli@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>