ARM: at91: add pmc DT support

Specified the main Oscillator via clock binding.
This will allow to do not hardcode it anymore in the DT board at 12MHz.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/mach-at91/setup.c

@@ -292,9 +292,8 @@ void __init at91_dt_initialize(void)
 	/* temporary until have the ramc binding*/
 	at91_boot_soc.ioremap_registers();
 
-	/* temporary until have the pmc binding */
 	/* Init clock subsystem */
-	at91_clock_init(12000000);
+	at91_dt_clock_init();
 
 	/* Register the processor-specific clocks */
 	at91_boot_soc.register_clocks();