ARM: dts: at91: sama5d3: add u-boot properties to sama5d3 pit timer

in the early SPL boot stage whenever there is a call to udelay,
dm_timer_init fails to find the pit timer whenever it traverses
the device tree, if this property is not present

Signed-off-by: Manuel Reis <mluis.reis@gmail.com>
CC: Eugen Hristev <eugen.hristev@microchip.com>
Tested-by: Derald D. Woods <woods.technical@gmail.com>
Reviewed-by: Eugen Hristev <eugen.hristev@microchip.com>