cortex_m3: change cortec_m3 reset_config behaviour

Currently the cmd 'cortex_m3 reset_config' will overide the default
target's 'reset_config'.
Chnage the behaviour to use the target 'reset_config' if configured and
fallback if not.

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

src/target/cortex_m3.h

@@ -136,7 +136,6 @@ struct cortex_m3_dwt_comparator
 
 enum cortex_m3_soft_reset_config
 {
-	CORTEX_M3_RESET_SRST,
 	CORTEX_M3_RESET_SYSRESETREQ,
 	CORTEX_M3_RESET_VECTRESET,
 };