cxgb4: dynamically determine flash size and FW image location

Handle the larger flash memories on newer boards:

- get the size and number of sectors by probing the flash
- writes and erases can take longer, adjust the timeouts for these operations
- the FW image can be at different locations depending on flash size,
  find its location dynamically as well.

Signed-off-by: Dimitris Michailidis <dm@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>