clk: Add CLK_HW_INIT_FW_NAME macro using .fw_name in .parent_data

With the new clk parenting code, clk_init_data was expanded to include
.parent_data, for clk drivers that have parents referenced using a
combination of device tree clock-names, clock indices, and/or clk_hw
pointers.

Add a CLK_HW_INIT macro for specifying a single parent from the device
tree using .fw_name in struct clk_parent_data.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>