vm: Increase the size of the boot partition

For the moment the kernel with initramfs is around 35M. If there are 3 successive updates that include kernel/initramfs updates, then for a short time the /boot disk will need to have 3 sets of kernels. This is more than 100M so it fails.

Also it is likely that the kernel and initramfs will slowly increase with the time. Resizing a boot partition is a bit too annoying for most people to do. So 500M should be a safe bet for a long time, rather than going for 200M.