cxgb4: Fix to dump devlog, even if FW is crashed

Add new Common Code routines to retrieve Firmware Device Log
parameters from PCIE_FW_PF[7]. The firmware initializes its Device Log very
early on and stores the parameters for its location/size in that register.
Using the parameters from the register allows us to access the Firmware
Device Log even when the firmware crashes very early on or we're not
attached to the firmware

Based on original work by Casey Leedom <leedom@chelsio.com>

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>