cxgb4: Replaced the backdoor mechanism to access the HW memory with PCIe Window method

Rip out a bunch of redundant PCI-E Memory Window Read/Write routines,
collapse the more general purpose routines into a single routine
thereby eliminating the need for a large stack frame (and extra data
copying) in the outer routine, change everything to use the improved
routine t4_memory_rw.

Based on origninal work by Casey Leedom <leedom@chelsio.com> and
Steve Wise <swise@opengridcomputing.com>

Signed-off-by: Casey Leedom <leedom@chelsio.com>
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>