cactus: add exception/interrupt framework

This patch adds following changes to cactus
 1. Set up exception vector base address.
 2. Add skeleton interrupt handler.
 3. Install default tftf cpu exception handler.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: I265553918b45a0e7e80ef0d7c48c09abfbec1a5f
3 files changed