arm: semihosting: set command line arguments

Add "arm semihosting_cmdline [argv0 argv1 ...]" for setting the
command line arguments for the debuggee.

[andreas.fritiofson@gmail.com]: Dynamic allocation, empty default

Change-Id: I831ddd161d602f251940e29608a154e9590fdee1
Signed-off-by: Christian Groessler <chris@groessler.org>
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/3106
Tested-by: jenkins

src/target/arm.h

@@ -157,6 +157,9 @@ struct arm {
 
 	int (*setup_semihosting)(struct target *target, int enable);
 
+	/** Semihosting command line. */
+	char *semihosting_cmdline;
+
 	/** Backpointer to the target. */
 	struct target *target;