drivers/can: stm32_fd: convert domain clk src sel. from kconfig to dts

Use domain clocks if they are defined in dts.

Until now domain clock sources could be selected via kconfig.
STM32 platform now can configure domain clock sources via
clock control driver, therefore this commit makes use of it.

The configuration is shared between canfd instances, so a domain clock
has to be defined for only one instance. Otherwise, only the
configuration from the latest initialized instance will remain.

The dependency on clock source PCLK1 for CAN_STM32FD_CLOCK_DIVISOR
was removed, because the divider also divides other clocks.
Note that setting that divider does not work at all at the moment,
because the write protection is not disabled.

Signed-off-by: Thomas Stranger <thomas.stranger@outlook.com>