fdt_support: Make of_bus_default_count_cells non static

of_bus_default_count_cells can be used to get the #address-cells
and #size-cells defined by the current node's parent node. This
is required when using of_read_number to read from FDT nodes that
can be 32 or 64 bytes depending on values defined by the parent.

Signed-off-by: Arnab Basu <arnab.basu@freescale.com>
CC: Scott Wood <scottwood@freescale.com>