Add support for %p in tf_printf()

This patch adds support for the `%p` format specifier in tf_printf()
following the example of the printf implementation of the stdlib used
in the trusted firmware.

Fixes ARM-software/tf-issues#292

Change-Id: I0b3230c783f735d3e039be25a9405f00023420da
diff --git a/drivers/arm/gic/gic_v3.c b/drivers/arm/gic/gic_v3.c
index f429662..11185b2 100644
--- a/drivers/arm/gic/gic_v3.c
+++ b/drivers/arm/gic/gic_v3.c
@@ -60,8 +60,8 @@
 			/* Disable this print for now as it appears every time
 			 * when using PSCI CPU_SUSPEND.
 			 * TODO: Print this only the first time for each CPU.
-			 * INFO("GICv3 - Found RDIST for MPIDR(0x%lx) at 0x%lx\n",
-			 *	mpidr, addr);
+			 * INFO("GICv3 - Found RDIST for MPIDR(0x%lx) at %p\n",
+			 *	mpidr, (void *) addr);
 			 */
 			return addr;
 		}