ctf: fix CONFIG_CTF && !CONFIG_DTRACE and CONFIG_DT_DISABLE_CTF

ctf: fix CONFIG_CTF && !CONFIG_DTRACE and CONFIG_DT_DISABLE_CTF

These combinations of config options, one of which should enable
CTF without enabling DTrace, the other one of which should enable
DTrace without enabling CTF, are both broken.

Fix them by making the CTF <-> DT_DISABLE_CTF relationship bidirectional,
by making dwarf2ctf compilation depend properly on CONFIG_CTF rather than
CONFIG_DTRACE, and by fixing the newly-introduced order-only dependency
of CTF on the sdtinfo stubs files so that it is only enforced when
both CTF and DTrace are enabled.

Orabug: 23859082
Signed-off-by: Nick Alcock <nick.alcock@oracle.com>
Reviewed-By: Todd Vierling <todd.vierling@oracle.com>