drm_hwcomposer: Move HardwareSupportsLayerType into Backend

The HardwareSupportsLayerType function is used only for display validation
which is implemented in the generic backend.

Signed-off-by: Matvii Zorin <matvii.zorin@globallogic.com>
diff --git a/backend/Backend.cpp b/backend/Backend.cpp
index c7e78c9..4c2a931 100644
--- a/backend/Backend.cpp
+++ b/backend/Backend.cpp
@@ -93,13 +93,18 @@
 
 bool Backend::IsClientLayer(DrmHwcTwo::HwcDisplay *display,
                             DrmHwcTwo::HwcLayer *layer) {
-  return !display->HardwareSupportsLayerType(layer->sf_type()) ||
+  return !HardwareSupportsLayerType(layer->sf_type()) ||
          !BufferInfoGetter::GetInstance()->IsHandleUsable(layer->buffer()) ||
          display->color_transform_hint() != HAL_COLOR_TRANSFORM_IDENTITY ||
          (layer->RequireScalingOrPhasing() &&
           display->resource_manager()->ForcedScalingWithGpu());
 }
 
+bool Backend::HardwareSupportsLayerType(HWC2::Composition comp_type) {
+  return comp_type == HWC2::Composition::Device ||
+         comp_type == HWC2::Composition::Cursor;
+}
+
 uint32_t Backend::CalcPixOps(const std::vector<DrmHwcTwo::HwcLayer *> &layers,
                              size_t first_z, size_t size) {
   uint32_t pixops = 0;