remove 'flash-kernel' hacks

We no longer bother to remove old versions of the flash-kernel hook.

Also remove the link to flash-kernel - we can replace it with a dh
links file if we absolutely need it back.

Signed-off-by: Matt Sealey <matt@genesi-usa.com>
add initramfs update hook

This is needed now that initramfs-tools no longer calls flash-kernel
internally.

Signed-off-by: Matt Sealey <matt@genesi-usa.com>
set architecture to 'any'

Signed-off-by: Matt Sealey <matt@genesi-usa.com>
add which-blockdev and make prep-kernel use it (fixes /dev/root)

While we are there, some minor cleanups were in order.

Signed-off-by: Matt Sealey <matt@genesi-usa.com>