meson: fix pl111 dependency on vc4

src/gallium/winsys/pl111/drm/libpl111winsys.a(pl111_drm_winsys.c.o): In function `pl111_drm_screen_create':
pl111_drm_winsys.c:(.text+0x33): undefined reference to `vc4_drm_screen_create_renderonly'

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>

meson.build

@@ -190,6 +190,9 @@ endif
 if with_gallium_imx and not with_gallium_etnaviv
   error('IMX driver requires etnaviv driver')
 endif
+if with_gallium_pl111 and not with_gallium_vc4
+  error('pl111 driver requires vc4 driver')
+endif
 
 dep_libdrm_intel = []
 if with_dri_i915 or with_gallium_i915