ARM: at91: PIT: Follow the general coding rules

ARM: at91: PIT: Follow the general coding rules

Replace all masks and bits definitions by matching calls to BIT and GENMASK.
While we're at it, also fix a few style issues.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>