d/initramfs/hooks/cryptroot: Add kernel modules named after IV generators

On 5.4 kernels ESSIV isn't implemented in dm_crypt but by a dedicated
'essiv' module which thus needs to be available in order to unlock
dm-crypt targets using 'aes-cbc-essiv:sha256' (the default cipher
specification for LUKS devices before cryptsetup 2:1.6.1-1).

Closes: #948593