meson: install vulkan_intel.h header

Fixes: d1992255bb
       ("meson: Add build Intel "anv" vulkan driver")
Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

include/meson.build

@@ -106,3 +106,7 @@ if with_gallium_opencl and not with_opencl_icd
     subdir: 'CL'
   )
 endif
+
+if with_intel_vk
+  install_headers('vulkan/vulkan_intel.h', subdir : 'vulkan')
+endif