Trusted Firmware currently has no support for secure self-hosted
debug.  To avoid unexpected exceptions, disable software debug
exceptions, other than software breakpoint instruction exceptions,
from all exception levels in secure state.  This applies to both
AArch32 and AArch64 EL3 initialization.

Change-Id: Id097e54a6bbcd0ca6a2be930df5d860d8d09e777
Signed-off-by: dp-arm <dimitris.papastamos@arm.com>