drm_hwcomposer: Add platform backend for minigbm

This adds support for the chromiumos (not AOSP) version of minigbm. Like
hisi, the gralloc handle is not the same as the common libdrm handle
(just yet), so we do need a separate backend for now.

Tested with a pending change to the 'cuttlefish' android virtual device
in AOSP with its custom gralloc switched to minigbm.

Cc: John Stultz <john.stultz@linaro.org>
Cc: Rob Herring <rob.herring@linaro.org>
Cc: Sean Paul <seanpaul@google.com>
Cc: Greg Hartman <ghartman@google.com>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Alistair Strachan <astrachan@google.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

diff --git a/Android.mk b/Android.mk
index 573c5aa..c0a1d0e 100644
--- a/Android.mk
+++ b/Android.mk
@@ -80,15 +80,16 @@
 LOCAL_CPPFLAGS += -DUSE_HISI_IMPORTER
 LOCAL_SRC_FILES += platformhisi.cpp
 LOCAL_C_INCLUDES += device/linaro/hikey/gralloc960/
-else
-ifeq ($(TARGET_PRODUCT),hikey)
+else ifeq ($(TARGET_PRODUCT),hikey)
 LOCAL_CPPFLAGS += -DUSE_HISI_IMPORTER
 LOCAL_SRC_FILES += platformhisi.cpp
 LOCAL_C_INCLUDES += device/linaro/hikey/gralloc/
+else ifeq ($(strip $(BOARD_DRM_HWCOMPOSER_BUFFER_IMPORTER)),minigbm)
+LOCAL_SRC_FILES += platformminigbm.cpp
+LOCAL_C_INCLUDES += external/minigbm/cros_gralloc/
 else
 LOCAL_CPPFLAGS += -DUSE_DRM_GENERIC_IMPORTER
 endif
-endif
 
 LOCAL_MODULE := hwcomposer.drm
 LOCAL_MODULE_TAGS := optional