Commit e74afb65 (Deprecate weak crash console functions) deprecated the
default inclusion of weak definitions for plat_crash_console functions
in plat/common/aarch64/platform_helpers.S. The code was later copied out
to plat/common/aarch64/crash_console_helpers.S so platforms can link it
explicitly if they want to. However, since deprecation does not mean
removal, the same code is also still duplicated in platform_helpers.S.

The duplicated code contains both empty stubs for the !MULTI_CONSOLE_API
case, and a real implementation that used to work but was broken by
commit d35cc347

 (Console: Use callee-saved registers) for
MULTI_CONSOLE_API. It's not great to have both of these duplicated in
two files, so this patch splits them up: in platform_helpers.S we'll
only keep the empty stubs (guarded by !ERROR_DEPRECATED), which should
not regress functionality since the MULTI_CONSOLE_API implementation was
already broken anyway. In crash_console_helpers.S, we'll only keep the
MULTI_CONSOLE_API version, which is enough both as an implementation in
itself and as a sample for how to reimplement these functions in a
platform-specific file.

Change-Id: I83d95a90ab6aac597dc2ea2f2797ac2c8ed075d4
Signed-off-by: Julius Werner <jwerner@chromium.org>