clocksource: ti-32k: make it depend on GENERIC_CLOCKSOURCE

the new ti 32k clocksource driver should depend on
GENERIC_CLOCKSOURCE because of its reliance on
sched_clock_register().

Let's enable that to avoid any possible build errors
and/or warnings on randbuilds.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>