cxgb4: Dynamically allocate memory in t4_memory_rw() and get_vpd_params()

This patch changes memory allocation to reduce stack footprint

Signed-off-by: Jay Hernandez <jay@chelsio.com>
Signed-off-by: Vipul Pandya <vipul@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>