drivers: i2c_ll_stm32_v2: don't use while loops in interrupt mode

Waiting for transfer complete and stop condition uses while loops
even when interrupt mode is enabled.
Implement use of TC, TCR and STOP interrupt for interrupt mode.
msg_done is not needed in interrupt mode anymore, so move it
to non-interrupt section
Tested with stm32f3_disco board.

Signed-off-by: Daniel Wagenknecht <wagenknecht@clage.de>