Some STM32F4xx chips have an R division factor in PLL. Add possibility
to configure that.
Even though the output from the R division is not used, it can be
increased to reduce power consumption.
Signed-off-by: Dawid Niedzwiecki <dawidn@google.com>
DTS property attributes are (by default) not required.
Explicitly specifying `required: false` is redundant.
Perhaps a warning to that effect would be useful.
Signed-off-by: Chris Friedt <cfriedt@meta.com>
Dawid Niedzwiecki