tcl/target: add CC2538 and CC26xx target files (with cJTAG procedure)

Added support for the Cortex-M3 based TI low power RF SoC CC2538 and
the CC26xx family.

These chips need a start sequence for switching from cJTAG to JTAG
before being used with OpenOCD, this is done in the tcl proc
ti_cjtag_to_4pin_jtag in the ti-cjtag.cfg config.

The configs for CC2538 and CC26xx run the start sequence on post-reset
event and set the ICEPick IDCODE in the data register for OpenOCD to
read, this is done so that every time OpenOCD resets the device, it
will enable JTAG.

Change-Id: I7db620211c0e7e03fad59d24fe31d23a9cdcfedc
Signed-off-by: Jacob Palsson <jaaacke@gmail.com>
Reviewed-on: http://openocd.zylin.com/2232
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>

tcl/target/cc2538.cfg

@@ -0,0 +1,16 @@
+# Config for Texas Instruments low power RF SoC CC2538
+# http://www.ti.com/lit/pdf/swru319
+
+if { [info exists CHIPNAME] } {
+   set CHIPNAME $CHIPNAME
+} else {
+   set CHIPNAME cc2538
+}
+
+if { [info exists JRC_TAPID] } {
+   set JRC_TAPID $JRC_TAPID
+} else {
+   set JRC_TAPID 0x8B96402F
+}
+
+source [find target/cc26xx.cfg]