board/radxa/rockpi-n8:use partition-type-uuid for genimage-15

Genimage 15 restricted the partition-type option to mbr and hybrid
partition-table-type and now prints a warning when it is used [1]:

ERROR: hdimage(disk.img): part boot: 'partition-type' is only valid for mbr and hybrid partition-table-type

[1] https://github.com/pengutronix/genimage/commit/1d72d8091f83790a0a35a1ea7dc25d46adba8876

So let's use for EFI System partition:
'partition-type-uuid = c12a7328-f81f-11d2-ba4b-00a0c93ec93b'
and for Root partition (32-bit ARM):
'partition-type-uuid = 69DAD710-2CE4-4E3C-B16C-21A1D49ABED3'

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/1929717242

FTR, the magic UUID are from:
    https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_type_GUIDs

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

board/radxa/rockpi-n8/genimage.cfg

@@ -26,14 +26,14 @@ image sdcard.img {
 	}
 
 	partition boot {
-		partition-type = 0xC
+		partition-type-uuid = c12a7328-f81f-11d2-ba4b-00a0c93ec93b
 		bootable = "true"
 		image = "boot.vfat"
 		offset = 16M
 	}
 
 	partition rootfs {
-		partition-type = 0x83
+		partition-type-uuid = 69dad710-2ce4-4e3c-b16c-21a1d49abed3
 		image = "rootfs.ext4"
 	}
 }