clocksource/drivers/fttmr010: Just count down

All timers can handled just counting down so what about just
doing that instead of special-casing the counting down mode.

This has the upside that overflow cannot occur so we can
remove some handling of that interrupt as well.

Cc: Cédric Le Goater <clg@kaod.org>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
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ChangeLog v1->v2:
- New patch.
1 file changed