package/mesa3d-demos: depend on vulkan-loader if enabled

Vulkan support in mesa3d-demos requires vulkan-loader. Without an
explicit config flag it is autodetected, and may or may not be enabled
depending on build order, leading to unpredictable results.

Fix this by explicitly enabling Vulkan support and depending on
vulkan-loader if BR2_PACKAGE_VULKAN_LOADER=y, and disabling Vulkan
support otherwise.

Signed-off-by: Fiona Klute (WIWA) <fiona.klute@gmx.de>
Signed-off-by: Julien Olivain <ju.o@free.fr>
(cherry picked from commit 7a55e82cb80c971370010df6a5513a7e565f1a72)
Signed-off-by: Thomas Perale <thomas.perale@mind.be>

package/mesa3d-demos/mesa3d-demos.mk

@@ -69,4 +69,11 @@ else
 MESA3D_DEMOS_CONF_OPTS += -Dwayland=disabled
 endif
 
+ifeq ($(BR2_PACKAGE_VULKAN_LOADER),y)
+MESA3D_DEMOS_DEPENDENCIES += vulkan-loader
+MESA3D_DEMOS_CONF_OPTS += -Dvulkan=enabled
+else
+MESA3D_DEMOS_CONF_OPTS += -Dvulkan=disabled
+endif
+
 $(eval $(meson-package))