Add flags for minigbm backends in BUILD.gn

This will allow configuring minigbm via GN variables, instead of make
file args.

Bug: 733450
Change-Id: I455d6b39c587b061a3527b63c7b1a1f556a529ac
Reviewed-on: https://chromium-review.googlesource.com/933595Reviewed-by: Michael Spang <spang@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Commit-Queue: Sergey Volk <servolk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538857}

third_party/minigbm/BUILD.gn

@@ -12,14 +12,59 @@ declare_args() {
   # system version, but when building on dev workstations or the Chrome
   # waterfall we bundle it because Ubuntu doesn't ship a usable version.
   use_system_minigbm = false
+
+  use_amdgpu_minigbm = false
+  use_amlogic_minigbm = false
+  use_exynos_minigbm = false
   use_intel_minigbm = false
+  use_marvell_minigbm = false
+  use_mediatek_minigbm = false
+  use_msm_minigbm = false
+  use_radeon_minigbm = false
+  use_rockchip_minigbm = false
+  use_tegra_minigbm = false
+  use_vc4_minigbm = false
 }
 
 if (!use_system_minigbm) {
   config("minigbm_config") {
     include_dirs = [ "src" ]
+    defines = []
+    if (use_amdgpu_minigbm) {
+      defines += [ "DRV_AMDGPU" ]
+    }
+    if (use_amlogic_minigbm) {
+      defines += [ "DRV_AMLOGIC" ]
+    }
+    if (use_exynos_minigbm) {
+      defines += [ "DRV_EXYNOS" ]
+    }
     if (use_intel_minigbm) {
-      defines = [ "DRV_I915" ]
+      defines += [ "DRV_I915" ]
+    }
+    if (use_marvell_minigbm) {
+      defines += [ "DRV_MARVELL" ]
+    }
+    if (use_mediatek_minigbm) {
+      defines += [ "DRV_MEDIATEK" ]
+    }
+    if (use_msm_minigbm) {
+      defines += [ "DRV_MSM" ]
+    }
+    if (use_msm_minigbm) {
+      defines += [ "DRV_MSM" ]
+    }
+    if (use_radeon_minigbm) {
+      defines += [ "DRV_RADEON" ]
+    }
+    if (use_rockchip_minigbm) {
+      defines += [ "DRV_ROCKCHIP" ]
+    }
+    if (use_tegra_minigbm) {
+      defines += [ "DRV_TEGRA" ]
+    }
+    if (use_vc4_minigbm) {
+      defines += [ "DRV_VC4" ]
     }
   }