999-cpc-fixes: enable more code on grub2 armhf & arm64

armhf & arm64 images use grub. And despite disk-image &
disk-image-uefi installing all the grubs, some of the configuration is
done in the 999-cpc-fixes. Specifically removal of "quiet splash" is
done there, but not active on armhf & arm64. This results in arm
images to boot with "quiet splash".

Enable running the later portions of 999-cpc-fixes on armhf & arm64.

Drop duplicate call to update-grub, as update-grub2 is simply a
symlink to update-grub.

Add a guard around the call to reconfigure grub-pc, to only do that
when it is installed.

This makes armhf & arm64 uefi images consistent with amd64 uefi
images.

LP: #1925780

live-build/ubuntu-cpc/hooks.d/chroot/999-cpc-fixes.chroot

@@ -117,7 +117,7 @@ fi
 
 case $arch in
 	# ARM, ppc, riscv64 and s390x images are special
-	armhf|arm64|powerpc|ppc64el|s390x|riscv64)
+	powerpc|ppc64el|s390x|riscv64)
 		exit 0
 		;;
 esac
@@ -208,17 +208,20 @@ GRUB_CMDLINE_LINUX_DEFAULT="console=tty1 console=ttyS0"
 # Set the grub console type
 GRUB_TERMINAL=console
 EOF
-_xchroot "${rootd}" update-grub2
 
-# since this is a disk image, we technically don't need to install all the
+# Sometimes grub is not installed yet (i.e. uefi arm images). Overall
-# grub modules, as the image itself is not bootable. This makes for a small
+# it is odd that we run this out of chroot hooks, instead of binary
-# disk image
+# hooks. I wonder if we can move all of this to disk-image hooks.
-_xchroot "${rootd}" update-grub
+if [ -x "${rootd}/usr/sbin/update-grub" ]; then
+    _xchroot "${rootd}" update-grub
+fi
 
 # reconfigure grub so that upgrades to grub-pc do not force a debconf config
 # changed prompt (LP: #1009294).  This re-runs update-grub
-_xchroot "${rootd}" env DEBIAN_FRONTEND=noninteractive \
+if [ -n "`_xchroot "${rootd}" dpkg-query -W grub-pc 2>/dev/null`" ]; then
+    _xchroot "${rootd}" env DEBIAN_FRONTEND=noninteractive \
              dpkg-reconfigure grub-pc
+fi
 
 grub2cfg="${rootd}/boot/grub/grub.cfg"
 [ ! -f "${grub2cfg}" ] ||