kbuild/ctf: always build vmlinux when building CTF.

kbuild/ctf: always build vmlinux when building CTF.

Before now, a 'make modules' in a clean tree would neglect to build the built-in
objects and yield an empty objects.builtin, or no objects.builtin at all.

Correct generation of the CTF requires all the .o and .a files which go into
vmlinux, and a list of them in objects.builtin: without them, dwarf2ctf will
fail one way or the other.

While we're at it, remove all CTF-related references in the build system to
CONFIG_DTRACE and CONFIG_DT_DISABLE_CTF: CTF generation has been decoupled from
DTrace and has its own config symbol nowadays.

Orabug: 17397200
Signed-off-by: Jamie Iles <jamie.iles@oracle.com>
Signed-off-by: Nick Alcock <nick.alcock@oracle.com>