rpi3: Use new console APIs

Switch to the new console APIs enabled by setting MULTI_CONSOLE_API=1.

The crash console doesn't use this API, it uses internally the core
functions of the 16550 console.

`bl31_plat_runtime_setup` is no longer needed. When this platform port
was introduced, that function used to disable the console. It was needed
to override that behaviour. The new behaviour is to switch to the
runtime console. The console is registered for all scopes (boot, crash
and runtime) in `rpi3_console_init` so it is not needed to override the
default behaviour anymore.

Update documentation.

Change-Id: If2ee8f91044216183b7ef142e5c05ad6220ae92f
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/plat/rpi3/platform.mk b/plat/rpi3/platform.mk
index e201cee..2cb7a15 100644
--- a/plat/rpi3/platform.mk
+++ b/plat/rpi3/platform.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2013-2017, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -81,6 +81,9 @@
 # Enable new version of image loading
 LOAD_IMAGE_V2			:= 1
 
+# Use multi console API
+MULTI_CONSOLE_API		:= 1
+
 # Platform build flags
 # --------------------
 
@@ -110,6 +113,10 @@
   $(error Error: rpi3 needs LOAD_IMAGE_V2=1)
 endif
 
+ifneq (${MULTI_CONSOLE_API}, 1)
+  $(error Error: rpi3 needs MULTI_CONSOLE_API=1)
+endif
+
 ifeq (${ARCH},aarch32)
   $(error Error: AArch32 not supported on rpi3)
 endif