Add driver for AST2700 to initialize DRAM in SPL.
This patch also refactors the Kconfig dependency of
Aspeed DRAM drivers as some of them are shared among
the file structures of RV and ARM ISAs.
Signed-off-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>
Acked-by: Leo Yu-Chi Liang <ycliang@andestech.com>
