ARM: at91: Kconfig: implement PIT64B selection

Implement PIT64B selection thus it will be available for the necessary
targets (at the moment SAM9X60 and SAMA7G5) w/o the necessity to
specify it via defconfig. With this the current CONFIG_TIMER_OF
dependency of PIT64B driver could be removed.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>

arch/arm/mach-at91/Kconfig

@@ -165,6 +165,15 @@ config ATMEL_CLOCKSOURCE_TCB
 	  to make a single 32-bit timer.
 	  It can also be used as a clock event device supporting oneshot mode.
 
+config MICROCHIP_CLOCKSOURCE_PIT64B
+	bool "64-bit Periodic Interval Timer (PIT64B) support"
+	default SOC_SAM9X60 || SOC_SAMA7
+	select MICROCHIP_PIT64B
+	help
+	  Select this to get a high resolution clockevent (SAM9X60) or
+	  clocksource and clockevent (SAMA7G5) based on Microchip 64-bit
+	  Periodic Interval Timer.
+
 config HAVE_AT91_UTMI
 	bool