Platform/Socionext/DeveloperBox: add support for persistent capsules

Add support for PersistAcrossReset capsules, by setting the associated
PCD, and by enabling the warm reboot implementation that reenters PEI
with interrupts, caches and MMU disabled.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>