ram: thead: Add initial DDR controller support for TH1520

ram: thead: Add initial DDR controller support for TH1520

This patch cleans the vendor code of DDR initialization up, converts the
driver to fit in DM framework and use a firmware[1] packaged by binman to
ship PHY configuration.

Currently the driver is only capable of initializing the controller to
work with dual-rank 3733MHz LPDDR4, which is shipped by 16GiB variants
of LicheePi 4A boards and I could test with. Support for other
configurations could be easily added later.

Link: https://github.com/ziyao233/th1520-firmware
Signed-off-by: Yao Zi <ziyao@disroot.org>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>