ARM: dts: sti: update clkgen-pll entries in stih407-clock

The clkgen-pll driver now embed the clock names (assuming the
right compatible is used). Remove all clock-output-names property
and update when necessary the compatible.

Signed-off-by: Alain Volmat <avolmat@me.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>