Device: Remove overloaded pio_latency parameter

This patch removes the overloading of the parameter, which seems both
redundant, and possibly incorrect.

The PciConfigAll now also uses a Param.Latency rather than a
Param.Tick. For backwards compatibility it still sets the pio_latency
to 1 tick. All the comments have also been updated to not state that
it is in simticks when it is not necessarily the case.

src/dev/Device.py

@@ -40,7 +40,7 @@ class BasicPioDevice(PioDevice):
     type = 'BasicPioDevice'
     abstract = True
     pio_addr = Param.Addr("Device Address")
-    pio_latency = Param.Latency('1ns', "Programmed IO latency in simticks")
+    pio_latency = Param.Latency('1ns', "Programmed IO latency")
 
 class DmaDevice(PioDevice):
     type = 'DmaDevice'