arm: fix console parameter for ARM cloud-images

On armhf and arm64 the QEMU virt machine provides the serial console as an
emulated AMBA PrimeCell UART which the kernel refers to as /dev/ttyAMA0.

Consider this when constructing GRUB_CMDLINE_LINUX_DEFAULT in file
/etc/default/grub.d/50-cloudimg-settings.cfg (LP: #2036730).

Reviewed-by: Gauthier Jolly <gauthier.jolly@canonical.com>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

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

@@ -170,6 +170,16 @@ fi
 psuedo_grub_probe > "${gprobe}"
 chmod 755 "${gprobe}"
 
+case $arch in
+   armhf|arm64)
+      # QEMU virt machine provides AMBA PrimeCell UART
+      serial_console='ttyAMA0'
+      ;;
+   *)
+      serial_console='ttyS0'
+      ;;
+esac
+
 # for Quantal and later, use /etc/default/grub.d functionality
 # rather than modifying the grub configuration itself.
 # This avoids the mess of having to do dpkg stuff
@@ -186,7 +196,7 @@ GRUB_RECORDFAIL_TIMEOUT=0
 GRUB_TIMEOUT=0
 
 # Set the default commandline
-GRUB_CMDLINE_LINUX_DEFAULT="console=tty1 console=ttyS0"
+GRUB_CMDLINE_LINUX_DEFAULT="console=tty1 console=${serial_console}"
 
 # Set the grub console type
 GRUB_TERMINAL=console