Allow transports to override the selected target (hla configs unification)

This should allow to share common configs for both regular access and
high-level adapters.

Use the newly-added functionality in stlink and icdi drivers, amend
the configs accordingly.

Runtime-tested with a TI tm4c123g board.

Change-Id: Ibb88266a4ca25f06f6c073e916c963f017447bad
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
[gus@projectgus.com: context-specific deprecation warnings]
Signed-off-by: Angus Gratton <gus@projectgus.com>
[andrew.smirnov@gmail.com: additional nrf51.cfg mods]
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Tested-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>
Reviewed-on: http://openocd.zylin.com/1664
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>

tcl/target/efm32.cfg

@@ -0,0 +1,43 @@
+#
+# efm32 target
+#
+
+source [find target/swj-dp.tcl]
+
+if { [info exists CHIPNAME] } {
+   set _CHIPNAME $CHIPNAME
+} else {
+   set _CHIPNAME efm32
+}
+
+# Work-area is a space in RAM used for flash programming
+# By default use 2kB
+if { [info exists WORKAREASIZE] } {
+   set _WORKAREASIZE $WORKAREASIZE
+} else {
+   set _WORKAREASIZE 0x800
+}
+
+if { [info exists CPUTAPID] } {
+   set _CPUTAPID $CPUTAPID
+} else {
+   set _CPUTAPID 0x2ba01477
+}
+
+swj_newdap $_CHIPNAME cpu -expected-id $_CPUTAPID
+
+adapter_khz 1000
+
+set _TARGETNAME $_CHIPNAME.cpu
+target create $_TARGETNAME cortex_m -chain-position $_TARGETNAME
+
+$_TARGETNAME configure -work-area-phys 0x10000000 -work-area-size $_WORKAREASIZE -work-area-backup 0
+
+set _FLASHNAME $_CHIPNAME.flash
+flash bank $_FLASHNAME efm32 0 0 0 0 $_TARGETNAME
+
+if {![using_hla]} {
+   # if srst is not fitted use SYSRESETREQ to
+   # perform a soft reset
+   cortex_m reset_config sysresetreq
+}