clk: st: flexgen: embed soc clock outputs within compatible data

In order to avoid relying on the old style description via the DT
clock-output-names, add compatible data describing the flexgen
outputs clocks for all STiH407/STiH410 and STiH418 SOCs.

In order to ease transition between the two methods, this commit
introduce the new compatible without removing the old method.
Once DTs will be fixed, the method relying on DT clock-output-names
will be removed from this driver as well as old compatibles.
Signed-off-by: Alain Volmat <avolmat@me.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Link: https://lore.kernel.org/r/20210331201632.24530-3-avolmat@me.comSigned-off-by: Stephen Boyd <sboyd@kernel.org>