cxgb4: Remove duplicate register definitions

Removed duplicate definition for SGE_PF_KDOORBELL, SGE_INT_ENABLE3,
PCIE_MEM_ACCESS_OFFSET registers.
Moved the register field definitions around the register definition.

Signed-off-by: Santosh Rastapur <santosh@chelsio.com>
Signed-off-by: Vipul Pandya <vipul@chelsio.com>
Reviewed-by: Sivakumar Subramani <sivasu@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>