Add -gpu <mode> option to force GPU emulation

By default, GPU emulation is still disabled. You can
still try to force it with '-gpu on' for experimentation
purpose (alternatively, you can define hw.gpu.enabled to
'true' in your AVD config.ini)

Change-Id: I87efdf45337a80aeadd94b3922312b3f564c1608
diff --git a/android/main.c b/android/main.c
index 8fb9485..0b1d64c 100644
--- a/android/main.c
+++ b/android/main.c
@@ -1070,6 +1070,21 @@
         args[n++] = opts->memcheck;
     }
 
+    if (opts->gpu) {
+        const char* gpu = opts->gpu;
+        if (!strcmp(gpu,"on") || !strcmp(gpu,"enabled")) {
+            hw->hw_gpu_enabled = 1;
+        } else if (!strcmp(gpu,"off") || !strcmp(gpu,"disabled")) {
+            hw->hw_gpu_enabled = 0;
+        } else if (!strcmp(gpu,"auto")) {
+            /* Nothing to do */
+        } else {
+            derror("Invalid value for -gpu <mode> parameter: %s\n", gpu);
+            derror("Valid values are: on, off or auto\n");
+            exit(1);
+        }
+    }
+
     /* physical memory is now in hw->hw_ramSize */
 
     hw->avd_name = ASTRDUP(avdInfo_getName(avd));