clocksource: atmel-st: remove mach/hardware dependency

Remove the mach/hardware dependency to prepare the driver for multiplatform
support.
Also switch from setup_irq() to request_irq()

Signed-off-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>