[l1] Add rcc clock setup helper routines

Despite the L1 being a low power device, my initial focus is on making
it basically compatible with existing devices.

To that end, provide clock setup helper routines that configure it for maximum performance,
allowing some similar clock speeds to F1 devices to help with testing. This requires adding
the power chipset routines to set the voltage range.

Clock setup style is similar to the F4 code, which seems nicer than the overflow of different
routines used on the F1 code.

NOTE: Both the F4 existing pwr code, and this code don't actually include the f1 core power
code, even though it should be compatible