rtc: at91sam9: remove references to mach specific headers

In order to support multi platform kernel drivers should not include
machine specific headers.
Copy RTT macros in the driver code and remove any machine specific
headers.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Johan Hovold <johan@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>