drm/sprd: add Unisoc's drm display controller driver

Adds DPU(Display Processor Unit) support for the Unisoc's display
subsystem.
It's support multi planes, scaler, rotation, PQ(Picture Quality) and more.

v2:
- Use drm_xxx to replace all DRM_XXX.
- Use kzalloc to replace devm_kzalloc for sprd_dpu structure init.

v3:
- Remove dpu_layer stuff layer and commit layers by aotmic_update

v4:
- Use drmm_helpers to allocate crtc and planes.
- Move rotation enum definitions to crtc layer reg bitfields.
- Move allocate crtc and planes to bind function.

v5:
- Fix the checkpatch warnings.
- Use mode_set_nofb instead of mode_valid callback.
- Follow the OF-Graph bindings, use of_graph_get_port_by_id
instead of of_parse_phandle.
- Use zpos to represent the layer position.
- Rebase to last drm misc branch.

v6:
- Disable and clear interrupts before register dpu IRQ
- Init dpi config used by crtc_state->adjusted_mode on mode_set_nofb
- Remove enable_irq and disable_irq function call.
- Remove drm_format_info function call.

v7:
- Remove iommu error interrupt handling function.

Cc: Orson Zhai <orsonzhai@gmail.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
Signed-off-by: Kevin Tang <kevin.tang@unisoc.com>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211207142717.30296-5-kevin3.tang@gmail.com