cfg: enable stlink stm32l HSI

Switch to using the internal HSI when a reset init is called, this also
matches the std stm32l cfg.

Read (verify) speed is increased from 17 to 120 KiB/s.

Change-Id: Ic94ba85949ffdefa17b7be45eef14e30f941d107
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1004
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>

tcl/target/stm32lx_stlink.cfg

@@ -18,3 +18,18 @@ source [find target/stm32_stlink.cfg]
 
 set _FLASHNAME $_CHIPNAME.flash
 flash bank $_FLASHNAME stm32lx 0 0 0 0 $_TARGETNAME
+
+proc stm32l_enable_HSI {} {
+	# Enable HSI as clock source
+	echo "STM32L: Enabling HSI"
+
+	# Set HSION in RCC_CR
+	mww 0x40023800 0x00000101
+
+	# Set HSI as SYSCLK
+	mww 0x40023808 0x00000001
+}
+
+$_TARGETNAME configure -event reset-init {
+	stm32l_enable_HSI
+}