cpu, sim: Add param to force CPUs to wait for GDB

By setting the BaseCPU parameter wait_for_dbg_connection, the GDB
server blocks during initialisation waiting for the remote debugger to
connect before starting the simulated CPU.

Change-Id: I4d62c68ce9adf69344bccbb44f66e30b33715a1c
[ Update info message to include remote GDB port, rename param. ]
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/3963
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>

src/cpu/BaseCPU.py

@@ -151,6 +151,9 @@ class BaseCPU(MemObject):
     profile = Param.Latency('0ns', "trace the kernel stack")
     do_quiesce = Param.Bool(True, "enable quiesce instructions")
 
+    wait_for_remote_gdb = Param.Bool(False,
+        "Wait for a remote GDB connection");
+
     workload = VectorParam.Process([], "processes to run")
 
     if buildEnv['TARGET_ISA'] == 'sparc':