wsi: Add doc for the surface property interface

Change-Id: I9483b0fe7fbeafdc6ff2ae5d66da6762e373ab25
Signed-off-by: Rosen Zhelev <rosen.zhelev@arm.com>
1 job for dev/staging_wl in 1 minute and 9 seconds (queued for 39 seconds)
Status Job ID Name Coverage
  Test
passed #939364
build_vulkan_wsi_layer

00:01:09