Auto-detect mali DRI device path

When using exynos_drm, /dev/dri/card0 is now the exynos-drm node, and
/dev/dri/card1 is mali.

Instead of hardcoding mali at card0, use libdrm to automatically
provide the correct device node path.
Signed-off-by: Daniel Drake <drake@endlessm.com>

src/sunxi_mali_ump_dri2.c

@@ -1037,7 +1037,7 @@ SunxiMaliDRI2 *SunxiMaliDRI2_Init(ScreenPtr pScreen,
     info.version = 3;
 
     info.driverName = "lima";
-    info.deviceName = "/dev/dri/card0";
+    info.deviceName = drmGetDeviceNameFromFd(drm_fd);
     info.fd = drm_fd;
 
     info.CreateBuffer = MaliDRI2CreateBuffer;