Fix broken link in documentation
Fix broken link in documentation

The link to the exception handling framework page on the System Design /
Firmware Design / Section 4.3 just links to itself, so I changed it to
link to the exception handling framework component document.

Signed-off-by: John Powell <7f1289b8ac68c612804b1073274978986c0a7b3b@arm.com>
Change-Id: I6711b423a789b2b3d1921671e8497fffa8ba33d1

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware