aarch32: Add header shims to support old file locations

Out-of-tree code can still be using the old file locations. Introduce
header shims to include the headers from the new correct location and
print a warning message.

Add also a new Kconfig symbol to suppress such warning.

The shim will go away after two releases, so make sure to adapt your
application for the new locations.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>