ARM: configs: at91_dt_defconfig: configs for sam9x60

Enable CONFIG_NO_HZ_IDLE and CONFIG_HIGH_RES_TIMERS=y to be used
in conjunction with PIT64B present on SAM9X60.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210406141152.10706-1-claudiu.beznea@microchip.com