drivers: i2c_ll_stm32: Use I2C API flags

STM32 I2C driver doesn't use the I2C API flags STOP/RESTART,
instead it uses its own RESTART flag. As a result, I2C API's
i2c_burst_write* funtions doesn't work. This patch makes
STM32 I2C driver to use I2C API flags.

Tested on: 96b_carbon, olimexino_stm32 (i2c_ll_stm32_v1)
Tested on: stm32f3_disco, disco_l475_iot1 (i2c_ll_stm32_v2)

Fixes: #4459

Signed-off-by: Yannis Damigos <giannis.damigos@gmail.com>
Signed-off-by: Daniel Wagenknecht <wagenknecht@clage.de>