split startup.tcl file across modules

Moves definitions for each layer into their own file, eliminating
layering violations in the built-in TCL code.  Updates src/Makefile.am
rules to include all files in the final startup.tcl input file, and
others Makefile.am rules to distribute the new files in our packages.

src/server/startup.tcl

@@ -0,0 +1,8 @@
+# Handle GDB 'R' packet. Can be overriden by configuration script,
+# but it's not something one would expect target scripts to do
+# normally
+proc ocd_gdb_restart {target_id} {
+	# Fix!!! we're resetting all targets here! Really we should reset only
+	# one target
+	reset halt
+}