misc: 'sim{out/err}' -> 'sim{out/err}.txt'

By default, the --stderr-file and --stdout-file arguments were
directing the simulator output to files named "simerr" and
"simout" respectively if an output redirect was requested.

A small annoyance is these files lack an extension meaning programs
refuse to open them, or to do so without some additional effort. On
many systems they are assumed to scripts.

This patch adds the .txt extension to both, thus clearly indicating
to other programs these are text files and can be opened to be read
as such.

Change-Id: Iff5af4a9e6966b4467d005a029dbf401099fbd35

util/plot_dram/dram_sweep_plot.py

@@ -79,9 +79,9 @@ def main():
         exit(-1)
 
     try:
-        simout = open(sys.argv[2] + "/simout", "r")
+        simout = open(sys.argv[2] + "/simout.txt", "r")
     except IOError:
-        print("Failed to open ", sys.argv[2] + "/simout", " for reading")
+        print("Failed to open ", sys.argv[2] + "/simout.txt", " for reading")
         exit(-1)
 
     # Get the burst size, number of banks and the maximum stride from
@@ -102,7 +102,9 @@ def main():
     simout.close()
 
     if not got_sweep:
-        print("Failed to establish sweep details, ensure simout is up-to-date")
+        print(
+            "Failed to establish sweep details, ensure simout.txt is up-to-date"
+        )
         exit(-1)
 
     # Now parse the stats