ingenic-boot: Added package
od-rescue-cd: defconfig: Enable ingenic-boot
od-rescue-cd: Use system's ingenic-boot and change images dir
od-rescue-cd: Move the opendingux-bootdisc.sh script
od-rescue-cd: defconfig: Verify that images are installed
od-rescue-cd: Also mount /sys
od-rescue-cd: Drop support for the 512MB prototype unit

The 512 MiB GCW Zero prototype is unique, so it doesn't make
sense to support it.
od-rescue-cd: Propose to flash either system partition or all

Previously there was a huge issue: reflashing the MBR without the
data partition (which was the default behaviour) would lead to
a bricked system: the MBR would list the data partition as 800 MiB
but the ext4 filesystem can be much bigger (16 GiB by default on
retail GCW Zeros).