[PATCH v1] memory: mediatek: add DRAM controller driver

[Po-Kai Chi]

These patch series introduces the MediaTek DRAM controller driver (DRAMC)
on MT6779 SoC, and enables to be built as a module by default for the
ARM64 builds.

MediaTek DRAMC driver provides cross-platform features as below:
  - API provided to other kernel modules for querying DRAM type,
    rank count, rank size, channel count and mode register settings.
  - Sysfs interface used to pass DRAM mode register settings and current
    DRAM data rate to user-space for MediaTek ecosystem.

The API user includes MediaTek External Memory Interface (EMI) and
DVFS Resource Control (DVFSRC), which will be sent to mainline later.