cfg: allow stellaris device class override

Some devices, eg. The Tempest class return the wrong device class
when queried. Add the ability to manually override the device class.

Signed-off-by: Spencer Oliver <ntfreak@users.sourceforge.net>

tcl/target/stellaris.cfg

@@ -1,5 +1,17 @@
 # TI/Luminary Stellaris LM3S chip family
 
+# Some devices have errata in returning their device class.
+# DEVICECLASS is provided as a manual override
+# Manual setting of a device class of 0xff is not allowed
+
+global _DEVICECLASS
+
+if { [info exists DEVICECLASS ] } {
+   set _DEVICECLASS $DEVICECLASS
+} else {
+   set _DEVICECLASS 0xff
+}
+
 # Luminary chips support both JTAG and SWD transports.
 # Adapt based on what transport is active.
 source [find target/swj-dp.tcl]
@@ -74,7 +86,14 @@ $_TARGETNAME configure -event reset-start {
 	#	/openocd-development/2008-August/003065.html
 	#
 
-	set device_class [expr (([mrw 0x400fe000] >> 16) & 0xff)]
+	global _DEVICECLASS
+
+	if {$_DEVICECLASS != 0xff} {
+	   set device_class $_DEVICECLASS
+	} else {
+	   set device_class [expr (([mrw 0x400fe000] >> 16) & 0xff)]
+	}
+
 	if {$device_class == 0 || $device_class == 1 || $device_class == 3} {
 		# Sandstorm, Fury and DustDevil are able to use NVIC SYSRESETREQ
 		cortex_m3 reset_config sysresetreq