According to reference manuals both l0 and l4 have "v2" i2c peripheral.
This patch adds i2c support to l0 and l4 using previously unified "v2" i2c
headers and implementation.
No real hardware has been tested so far. Only compilation tests for both
libopencm3 and libopencm3-examples for all stm32 families.
Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>