drm/sprd: add Unisoc's drm kms master

Adds drm support for the Unisoc's display subsystem.

This is drm kms driver, this driver provides support for the
application framework in Android, Yocto and more.

Application framework can access Unisoc's display internal
peripherals through libdrm or libkms, it's test ok by modetest
(DRM/KMS test tool) and Android HWComposer.

v4:
  - Move the devm_drm_dev_alloc to master_ops->bind function.
  - The managed drmm_mode_config_init() it is no longer necessary for drivers to explicitly call drm_mode_config_cleanup, so delete it.

v5:
  - Remove subdir-ccflgas-y for Makefile.
  - Keep the selects sorted by alphabet for Kconfig.

Cc: Orson Zhai <orsonzhai@gmail.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
Signed-off-by: Kevin Tang <kevin.tang@unisoc.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211207142717.30296-3-kevin3.tang@gmail.com