tests: Add default DRAM class for riscv/x86 boot tests

These scripts can be quite useful for running quick boot tests. However,
having to specify the DRAM each time is laborious. A sensible default
has therefore been set.

Change-Id: I2714b479853f686246383411a46a98494ba617da
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/53848
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

tests/gem5/configs/riscv_boot_exit_run.py

@@ -80,7 +80,8 @@ parser.add_argument(
     "-d",
     "--dram-class",
     type=str,
-    required=True,
+    required=False,
+    default="DualChannelDDR3_1600",
     help="The python class for the memory interface to use"
 )
 

tests/gem5/configs/x86_boot_exit_run.py

@@ -78,7 +78,8 @@ parser.add_argument(
     "-d",
     "--dram-class",
     type=str,
-    required=True,
+    required=False,
+    default="DualChannelDDR3_1600",
     help="The python class for the memory interface to use"
 )
 parser.add_argument(