arm: omap2: timer: add a gptimer argument to sync32k_timer_init()

as it turns out, __omap_gptimer_init() and
__omap_sync32k_timer_init() are essentially
the same thing, but __omap_gptimer_init() wants
to always use gptimer.

Instead of forcing all those devices to pass
a use_gptimer cmdline argument, we add a new
function argument to __omap_sync32k_timer_init()
in preparation to deleting __omap_gptimer_init().

On a follow-up patch, we will remove uses of
__omap_gptimer_init() and replace them with
__omap_sync32k_timer_init() and pass the last
argument as true.

Signed-off-by: Felipe Balbi <balbi@ti.com>