Fix broken grub on crypto+lvm

Sometimes updates break your grub. Then I fix it with grml in the following way:

• Check your disks:

  fdisk -l

• Mount crypto volume:

  cryptsetup open /dev/nvme0n1p3 crypto

• activate all LVM volumes:

  vgchange -va y

• mount root:

  mount /dev/mapper/xxx-root /mnt

• mount boot and efi disks:

  mount /dev/nvme0n1p2 /mnt/boot
  mount /dev/nvme0n1p1 /mnt/boot/efi

• mount dev, sys and proc:

  mount --bind /dev /mnt/dev
  mount --bind /sys /mnt/sys
  mount --bind /proc /mnt/proc

• chroot into your system disk:

  chroot /mnt /bin/bash