Add openocd configuration

The target's debug would sometime get stuck while in low-power, making
it difficult to resume communications, even after hardware resets. Some
peripherals were also kept running when halted. This config should fix
these issues

openocd.cfg

@@ -0,0 +1,22 @@
+
+# using a STM32f103CB wich has 128kB of flash instead of the more common 64KB
+set CHIPNAME stm32f103CB
+set FLASH_SIZE 0x20000
+
+# load default configurations
+source [find interface/stlink.cfg]
+source [find target/stm32f1x.cfg]
+
+# override examine-end event
+$CHIPNAME.cpu configure -event examine-end {
+	# write DBGMCU_CR, disable all peripherals (timers, dmas, watchdogs while
+	# halted by debug. Trace is not affected
+	mmw 0xE0042004 0x7E3FFF07 0
+}
+
+# inits debugging, from that point, commands can be used
+init
+# resets the target and halt it immediately afterward. Stops debug from being
+# inacessible due to low-power states
+reset halt
+