target/dsp563xx: dsp563xx restore reg support

Added "exist=true" field to the reg_list struct to make access to the
dsp563xx registers again possible. Without it defaults to exist=false
and all the reg related functions will return nothing.

Fixes regression from b5964191f0

Change-Id: I9c256346735b8d66919c4ba83f528a8afca46ff9
Signed-off-by: Han Hartgers <han.hartgers@gmail.com>
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/5239
Tested-by: jenkins

src/target/dsp563xx.c

@@ -475,6 +475,7 @@ static void dsp563xx_build_reg_cache(struct target *target)
 		reg_list[i].value = calloc(1, 4);
 		reg_list[i].dirty = false;
 		reg_list[i].valid = false;
+		reg_list[i].exist = true;
 		reg_list[i].type = &dsp563xx_reg_type;
 		reg_list[i].arch_info = &arch_info[i];
 	}