Add missing dependencies & vmlinux symbolic link for Ubuntu

For `kpatch` to work on Ubuntu, kernel debug symbols `linux-image-$(uname -r)-dbgsym` package is required.

In addition, a `vmlinux` symbolic link needs to be created

`ln -s /usr/lib/debug/boot/vmlinux-$(uname -r) /usr/lib/debug/lib/modules/$(uname -r)/vmlinux`

for `kpatch-build` to work as per the following code

```bash
[[ -z $VMLINUX ]] && VMLINUX=/usr/lib/debug/lib/modules/${ARCHVERSION}/vmlinux
[[ -e "$VMLINUX" ]] || die "kernel-debuginfo not installed"
```