tcl: introduce using_(jtag|swd|hla) helpers and use them in reset handler

Barely tested with plain SWD transport.

Change-Id: I48b59136bf4294ffed737dba01f1b30ef83aa86b
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2003
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>

src/jtag/startup.tcl

@@ -21,7 +21,9 @@ proc jtag_init {} {
 # startup (at OpenOCD server startup, when JTAG may not yet work); and
 # potentially more (for reset types like cold, warm, etc)
 proc init_reset { mode } {
-	jtag arp_init-reset
+	if {[using_jtag]} {
+		jtag arp_init-reset
+	}
 }
 
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