[l1] Add Flash Memory Controller Register defns for L1.

Also, some of the most basic essential helper functions.
[l1] Add missing TIM5 bit from newer ref manual
[l1] Add PWR register definitions

Just the include file.
[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
[l1] Add common timer code support.

This has only been tested functionally with basic timers, and basic operations.
Advanced timer support has been #ifdefed to compile, but this probably needs more testing.
Merging pull request #67 L1 support: flash, power basics, timers

Merge remote-tracking branch 'karlp/pr_l1_flash-rcc-pwr-timers'