VIM1S: Use panfrost by default

Signed-off-by: Gunjan Gupta <viraniac@gmail.com>

config/boards/khadas-vim1s.conf

@@ -13,6 +13,7 @@ KHADAS_BOARD_ID="kvim1s" # used to compile the fip blobs
 declare -g KHADAS_OOWOW_BOARD_ID="VIM1S" # for use with EXT=output-image-oowow
 
 OVERLAY_PREFIX='s4-s905y4'
+DEFAULT_OVERLAYS="panfrost"
 
 function post_family_tweaks_bsp__populate_etc_firmware() {
 	# The hciattach command needs firmware to be placed in /etc/firmware directory.