docs(arm): add ARM_ROTPK_LOCATION variant full key

Updating documentation to reflect the new ARM_ROTPK_LOCATION variant of
the full ROTPK, as opposed to the hash of it.

Change-Id: I0f83c519bd607ef1270c7d30ee9bc55451ce4ae2
Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
2 files changed