boards: stm32: add flashing with stm32cubeprog for all

Add STM32CubeProgrammer where it is not available, & make it
default flashing method by placing it 1st in board.cmake

Before this change, the west runner that's selected when calling
'westflash' without the '--runner ...' option is kind of arbitrary
& depends on which runner is 1st in board.cmake file.

Another reason this change is needed is that STM32CubeProg is the only
available way to check/modify Option Bytes, and to flash code to
external Flash on many STM32 boards.

This change does not affect 'west debug' behavior, which defaults to
the debugger (OpenOCD/JLink) that is included first in board.cmake

Signed-off-by: Abderrahmane Jarmouni <git@jarmouni.me>