hw/intc/arm_gic: modernise the DPRINTF

While I was debugging the icount issues I realised a bunch of the
messages look quite similar. I've fixed this by including __func__ in
the debug print. At the same time I move the a modern if (GATE) style
printf which ensures the compiler can check for format string errors
even if the code gets optimised away in the non-DEBUG_GIC case.
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>

hw/intc/arm_gic.c

@@ -26,15 +26,20 @@
 #include "qemu/log.h"
 #include "trace.h"
 
-//#define DEBUG_GIC
+/* #define DEBUG_GIC */
 
 #ifdef DEBUG_GIC
-#define DPRINTF(fmt, ...) \
-do { fprintf(stderr, "arm_gic: " fmt , ## __VA_ARGS__); } while (0)
+#define DEBUG_GIC_GATE 1
 #else
-#define DPRINTF(fmt, ...) do {} while(0)
+#define DEBUG_GIC_GATE 0
 #endif
 
+#define DPRINTF(fmt, ...) do {                                          \
+        if (DEBUG_GIC_GATE) {                                           \
+            fprintf(stderr, "%s: " fmt, __func__, ## __VA_ARGS__);      \
+        }                                                               \
+    } while (0)
+
 static const uint8_t gic_id_11mpcore[] = {
     0x00, 0x00, 0x00, 0x00, 0x90, 0x13, 0x04, 0x00, 0x0d, 0xf0, 0x05, 0xb1
 };