Improve MULTI_CONSOLE_API deprecation warnings

For platforms that have not migrated to MULTI_CONSOLE_API == 1, there
are a lot of confusing deprecated declaration warnings relating to
use of console_init() and console_uninit(). Some of these relate to use
by the generic code, not the platform code. These functions are not really
deprecated but *removed* when MULTI_CONSOLE_API == 1.

This patch consolidates these warnings into a single preprocessor warning.
The __deprecated attribute is removed from the console_init() and
console_uninit() declarations.

For preprocessor warnings like this to not cause fatal build errors,
this patch adds -Wno-error=cpp to the build flags when
ERROR_DEPRECATED == 0.
This option (and -Wno-error=deprecated-declarations) is now added to
CPPFLAGS instead of TF_CFLAGS to ensure the build flags are used in the
assembler as well as the compiler.

This patch also disentangles the MULTI_CONSOLE_API and ERROR_DEPRECATED
build flags by defaulting MULTI_CONSOLE_API to 0 instead of
ERROR_DEPRECATED. This allows platforms that have not migrated to
MULTI_CONSOLE_API to use ERROR_DEPRECATED == 1 to emit a more meaningful
build error.

Finally, this patch bans use of MULTI_CONSOLE_API == 1 and AARCH32, since
the AArch32 console implementation does not support
MULTI_CONSOLE_API == 1.

Change-Id: If762165ddcb90c28aa7a4951aba70cb15c2b709c
Signed-off-by: Dan Handley <dan.handley@arm.com>
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index a80a491..751f834 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2016-2017, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2016-2018, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -98,9 +98,9 @@
 # Flag to enable new version of image loading
 LOAD_IMAGE_V2			:= 0
 
-# Use the new console API that allows registering more than one console instance
-# at once. Use = instead of := to dynamically default to ERROR_DEPRECATED.
-MULTI_CONSOLE_API		= $(ERROR_DEPRECATED)
+# Enable use of the console API allowing multiple consoles to be registered
+# at the same time.
+MULTI_CONSOLE_API		:= 0
 
 # NS timer register save and restore
 NS_TIMER_SWITCH			:= 0