clk: stm32: fix: stm32 clock drivers are not compiled by default

Clock driver is mandatory if the machine is selected.
Then don't use 'bool' and 'depends on' commands, but 'def_bool'
with the machine(s).

Fixes: da32d353

 ("clk: stm32: add configuration flags for each of the stm32 drivers")
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>