sp_min: Implement `sp_min_plat_runtime_setup()`

On ARM platforms before exiting from SP_MIN ensure that
the default console is switched to the runtime serial port.

Change-Id: I0ca0d42cc47e345d56179eac16aa3d6712767c9b
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>
diff --git a/include/plat/arm/common/plat_arm.h b/include/plat/arm/common/plat_arm.h
index 62c0ce7..e61c22f 100644
--- a/include/plat/arm/common/plat_arm.h
+++ b/include/plat/arm/common/plat_arm.h
@@ -163,6 +163,7 @@
 /* SP_MIN utility functions */
 void arm_sp_min_early_platform_setup(void *from_bl2,
 		void *plat_params_from_bl2);
+void arm_sp_min_plat_runtime_setup(void);
 
 /* FIP TOC validity check */
 int arm_io_is_toc_valid(void);