tm32_adc: Add STM32L152XX ADC support

Porting from Thingsee OS.

Credits: Dmitry Nikolaev wrote most of the code, Teemu Pirinen from Offcode Ltd.
contributed support for changing single shot adc channel, minor tweeks by
Jussi Kivilinna and Juha Niskanen

Signed-off-by: Juha Niskanen <juha.niskanen@haltian.com>

Includes additional changes from review.