cortex m3: add cortex_m3 reset_config cmd

This new cmd adds the ability to choose the Cortex-M3
reset method used.
It defaults to using SRST for reset if available otherwise
it falls back to using NVIC VECTRESET. This is known to work
on all cores.

Move any luminary specific reset handling to the stellaris cfg file.

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

doc/openocd.texi

@@ -6592,6 +6592,21 @@ must also be explicitly enabled.
 This finishes by listing the current vector catch configuration.
 @end deffn
 
+@deffn Command {cortex_m3 reset_config} (@option{srst}|@option{sysresetreq}|@option{vectreset})
+Control reset handling. The default @option{srst} is to use srst if fitted,
+otherwise fallback to @option{vectreset}.
+@itemize @minus
+@item @option{srst} use hardware srst if fitted otherwise fallback to @option{vectreset}.
+@item @option{sysresetreq} use NVIC SYSRESETREQ to reset system.
+@item @option{vectreset} use NVIC VECTRESET to reset system.
+@end itemize
+Using @option{vectreset} is a safe option for all current Cortex-M3 cores.
+This however has the disadvantage of only resetting the core, all peripherals
+are uneffected. A solution would be to use a @code{reset-init} event handler to manually reset
+the peripherals.
+@xref{Target Events}.
+@end deffn
+
 @anchor{Software Debug Messages and Tracing}
 @section Software Debug Messages and Tracing
 @cindex Linux-ARM DCC support