Many asserts depend on code that is conditionally compiled based on the
DEBUG define. This patch modifies the conditional inclusion of such code
so that it is based on the ENABLE_ASSERTIONS build option.

Change-Id: I6406674788aa7e1ad7c23d86ce94482ad3c382bd
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>