Add doc for some Cortex A53 errata workarounds

Add documentation for errata 835769 and 843419 workarounds introduced in
commit a94cc374ab57b80d86974f8771565d65b38403ef

Fixes ARM-software/tf-issues#504

Change-Id: I7f3db53dfc5f3827b32663f483d3302bc9679b19
Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>
1 file changed