arm: realm: Early memory setup

A Realm must mark areas of memory as RIPAS_RAM before an access is made.

The binary image is loaded by the VMM and thus the area is converted.
However, the file image may not cover tail portion of the "memory" image (e.g,
BSS, stack etc.). Convert the area touched by the early boot code to RAM
before the access is made in early assembly code.

Once, we land in the C code, we take care of converting the entire RAM region
to RIPAS_RAM.

Please note that this operation doesn't require the host to commit memory to
the Realm.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Co-developed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Co-developed-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Joey Gouly <joey.gouly@arm.com>