feat(arm): add ARM_ROTPK_LOCATION variant full key

feat(arm): add ARM_ROTPK_LOCATION variant full key

Add support for ARM_ROTPK_LOCATION=devel_full_dev_rsa_key, which
implements the scenario where the platform provides the full ROTPK, as
opposed to the hash of it. This returns a 2kB development RSA key
embedded into the firmware.

The motivation for this patch is to extend our test coverage in the CI.
Right now, the authentication framework allows platforms to return
either the full ROTPK or a hash of it (*). However, the FVP platform
only supports returning a hash currently so we cannot easily exercise
the full key scenario. This patch adds that capability.

(*) Or even no key at all if it's not deployed on the platform yet, as
is typically the case on pre-production/developement platforms.

Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
Change-Id: Ie869cca1082410e63894e2b7dea2d31155684105