sunxi: A23/A33/H3: Move sun8i secure monitor to SRAM A2

So far for the H3, A23, and A33 SoCs, we use DRAM to hold the secure
monitor code (providing PSCI runtime services). And while those SoCs do
not have the secure SRAM B like older SoCs, there is enough (secure)
SRAM A2 to put the monitor code and data in there instead.

Follow the design of 64-bit SoCs and use the first part for the monitor,
and the last 16 KiB for the SCP firmware. With this change, the monitor
no longer needs to reserve a region in DRAM.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
[Andre: amend commit message, fix R40 and V3s build]
Signed-off-by: Andre Przywara <andre.przywara@arm.com>