ARM: at91/clocksource: remove !DT PIT initializations

As AT91 !DT code is now removed, cleanup the PIT clocksource driver.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[nicolas.ferre@atmel.com: split patch]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Boris BREZILLON <boris.brezillon@free-electrons.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>