cfg: EFM32 supports SYSRESETREQ so use it

Change-Id: If52fdea025a2f9620ad4ddacfb83cbb83a94944d
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1541
Tested-by: jenkins

tcl/target/efm32_stlink.cfg

@@ -22,7 +22,7 @@ if { [info exists CPUTAPID] } {
    set _CPUTAPID 0x2ba01477
 }
 
-# EFM32 MCUs only support SW interface
+# EFM32 MCUs only support SWD interface
 set _TRANSPORT hla_swd
 
 transport select $_TRANSPORT
@@ -36,3 +36,7 @@ $_TARGETNAME configure -work-area-phys 0x10000000 -work-area-size $_WORKAREASIZE
 
 set _FLASHNAME $_CHIPNAME.flash
 flash bank $_FLASHNAME efm32 0 0 0 0 $_TARGETNAME
+
+# if srst is not fitted use SYSRESETREQ to
+# perform a soft reset
+cortex_m reset_config sysresetreq