cpc/UEFI: name the GPT partition cloudimg-rootfs

To boot initrdless, the kernel supports a limited number of ways to
specify the location of the root filesystem[1]. One of them is to use
the PARTUUID (which will be different for every cloud-image), another is
to use the PARTLABEL (partition name). To allow the use of PARTLABEL in
the kernel command line and make our cloud-images more self-describing,
set the PARTLABEL to cloudimg-rootfs which is the same label we use for
the file system inside this partition.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/early-lookup.c#n217

live-build/ubuntu-cpc/hooks.d/base/disk-image-ppc64el.binary

@@ -25,6 +25,7 @@ create_partitions() {
         --new=2::+8M \
         --new=1:
     sgdisk "${disk_image}" \
+        --change-name=1:"$FS_LABEL" \
         -t 2:4100 \
         -t 1:"$(gpt_root_partition_uuid $ARCH)"
     sgdisk "${disk_image}" \

live-build/ubuntu-cpc/hooks.d/base/disk-image-uefi.binary

@@ -42,6 +42,7 @@ create_partitions() {
                    --new=13::1G \
                    --typecode=13:ea00 \
                    --new=1: \
+                   --change-name=1:"$FS_LABEL" \
                    --typecode=1:"$(gpt_root_partition_uuid $ARCH)"
             ;;
         riscv64)
@@ -52,6 +53,7 @@ create_partitions() {
                    --new=15::+106M \
                    --typecode=15:ef00 \
                    --new=1:: \
+                   --change-name=1:"$FS_LABEL" \
                    --typecode=1:"$(gpt_root_partition_uuid $ARCH)" \
                    --attributes=1:set:2
             ;;
@@ -63,6 +65,7 @@ create_partitions() {
                    --new=15::+106M \
                    --new=1::
             sgdisk "${disk_image}" \
+                   --change-name=1:"$FS_LABEL" \
                    -t 14:ef02 \
                    -t 15:ef00 \
                    -t 1:"$(gpt_root_partition_uuid $ARCH)"