clocksource/drivers/timer-ti-dm: Make driver selection bool for TI K3

clocksource/drivers/timer-ti-dm: Make driver selection bool for TI K3

The clocksource drivers do not currently have loadable modules as
pointed out by Daniel Lezcano <daniel.lezcano@linaro.org>.

Let's reconsider this later on once timer removal discussion has been
done, and set timer-ti-dm to bool for TI K3 SoC.

Cc: Keerthy <j-keerthy@ti.com>
Cc: Nishanth Menon <nm@ti.com>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20220523151448.23732-1-tony@atomide.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>