fdt_support: Remove fdt_alloc_phandle() in favor of fdt_generate_phandle()

fdt_support: Remove fdt_alloc_phandle() in favor of fdt_generate_phandle()

Commit f0921f5098d ("fdt: Sync up to the latest libfdt") introduced
fdt_generate_phandle() in libfdt, making fdt_alloc_phandle() obsolete in
fdt_support.

Signed-off-by: Marek Behún <[email protected]>
Reviewed-by: Stefan Roese <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: "hui.song" <[email protected]>
Cc: Meenakshi Aggarwal <[email protected]>
Cc: Priyanka Jain <[email protected]>
Cc: Ioana Ciornei <[email protected]>
Reviewed-by: Simon Glass <[email protected]>