stm32:l0: Correctly compile as m0+, not m0.

Committed to binutils back in 2012, so even though it has no real impact, it at
least does the right thing for future compilers to make better decisions.

Signed-off-by: Karl Palsson <karlp@tweak.net.au>
stm32:l0: Add RCC register definitions

Tested with a miniblink example on the l053 discovery board.

Only register definitions at this stage, no helpers.
Register definitions from RM0367r2, hopefully the biggest
superset of L0 parts.

Signed-off-by: Karl Palsson <karlp@tweak.net.au>
stm32:l0: Add linker script / memory sizes

Easier to pick a corresponding part.
stm32:l0: rcc: add osc_on/osc_off helpers

These are the routines that have custom switch cases, and aren't easy targets
for pulling out.
NOUP: start the definitions of ppre1 extern stuff