egl: move alloc & init out of _eglBuiltInDriver{DRI2,Haiku}

This is a revert of Marek's 84f3afc2e122cb418573 revert, with a missing
line added back. I failed a rebase and dropped that crucial line, and
didn't do a runtime test after my rebase, and as a result broke EGL for
everyone.
This commit has been tested by Intel's CI and I re-read it once more, so
it should be good this time.
--

Note: dropping the EGL_BAD_ALLOC in egl_haiku because it's
overwritten by the EGL_NOT_INITIALIZED in eglInitialize().

Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
diff --git a/src/egl/drivers/dri2/egl_dri2.c b/src/egl/drivers/dri2/egl_dri2.c
index 8b482c9..e38459d 100644
--- a/src/egl/drivers/dri2/egl_dri2.c
+++ b/src/egl/drivers/dri2/egl_dri2.c
@@ -3255,16 +3255,11 @@
 
 /**
  * This is the main entrypoint into the driver, called by libEGL.
- * Create a new _EGLDriver object and init its dispatch table.
+ * Gets an _EGLDriver object and init its dispatch table.
  */
-_EGLDriver *
-_eglBuiltInDriver(void)
+void
+_eglInitDriver(_EGLDriver *dri2_drv)
 {
-   _EGLDriver *dri2_drv = calloc(1, sizeof *dri2_drv);
-   if (!dri2_drv)
-      return NULL;
-
-   _eglInitDriverFallbacks(dri2_drv);
    dri2_drv->API.Initialize = dri2_initialize;
    dri2_drv->API.Terminate = dri2_terminate;
    dri2_drv->API.CreateContext = dri2_create_context;
@@ -3316,6 +3311,4 @@
    dri2_drv->API.SetBlobCacheFuncsANDROID = dri2_set_blob_cache_funcs;
 
    dri2_drv->Name = "DRI2";
-
-   return dri2_drv;
 }