These two properties are necessary for SPL to get clocks from DT.
For now, only clock look-up by index is supported (clk_get_by_index()
function), so "clock-names" is never parsed in U-Boot. However, we
may want to support something like clk_get_by_name() in the future,
so let's keep "clock-names" as well as "clocks".
Signed-off-by: Masahiro Yamada <email@example.com>