egl/main: add support for fourth plane tokens

The EGL_EXT_dma_buf_import_modifiers extension adds support for a
fourth plane, just like DRM KMS API does.

Bump maximum dma_buf plane count to four.

v2: prevent attribute tokens from being parsed if
    EXT_image_dma_buf_import_modifiers is not suported. (Emil Velikov)

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Signed-off-by: Varad Gautam <varad.gautam@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
diff --git a/src/egl/drivers/dri2/egl_dri2.c b/src/egl/drivers/dri2/egl_dri2.c
index a2c9e41..8f0f1b3 100644
--- a/src/egl/drivers/dri2/egl_dri2.c
+++ b/src/egl/drivers/dri2/egl_dri2.c
@@ -2090,7 +2090,7 @@
     * "If <target> is EGL_LINUX_DMA_BUF_EXT, and the EGL_LINUX_DRM_FOURCC_EXT
     *  attribute indicates a single-plane format, EGL_BAD_ATTRIBUTE is
     *  generated if any of the EGL_DMA_BUF_PLANE1_* or EGL_DMA_BUF_PLANE2_*
-    *  attributes are specified."
+    *  or EGL_DMA_BUF_PLANE3_* attributes are specified."
     */
    for (i = plane_n; i < DMA_BUF_MAX_PLANES; ++i) {
       if (attrs->DMABufPlaneFds[i].IsPresent ||