leds: qti-flash: Do not enable flash without the timeout

When the user strobes a flash LED device with a timeout of 0, configure
the safety timer with default timeout to avoid turning flash ON for
long duration. Also clear different parameters of flash/torch device
like current, timeout when the device is disabled.

Change units of min, max, step of flash timeout to micro seconds as
flash LED class expects in micro seconds.

Change-Id: I780fb2639a1beda38e391e1e0818176f147175ef
Signed-off-by: Shyam Kumar Thella <sthella@codeaurora.org>