board/orangepi/orangepi-rk3399/genimage: fix partition types for gpt

Fixes the following error during image generation:
  ERROR: hdimage(sdcard.img): part boot: 'partition-type' is only valid
  for mbr and hybrid partition-table-type

Fixes: https://gitlab.com/buildroot.org/buildroot/-/jobs/2103784375

Signed-off-by: Marcus Hoffmann <marcus.hoffmann@othermo.de>
Reviewed-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

board/orangepi/orangepi-rk3399/genimage.cfg

@@ -26,14 +26,13 @@ image sdcard.img {
 	}
 
 	partition boot {
-		partition-type = 0xC
+		partition-type-uuid = F
 		bootable = "true"
 		image = "boot.vfat"
 		offset = 16M
 	}
 
 	partition rootfs {
-		partition-type = 0x83
 		image = "rootfs.ext4"
 	}
 }