i2s: stm32h7: add i2s support for stm32h7 mcu family

This commit modifies the I2S driver to work for STM32H7
family of MCU's. Currently only TX is working.

Tested on nucleo_stm32h743zi. Requires dma1 & dmamux1 to be enabled.

Signed-off-by: Emil Lindqvist <emil@lindq.gr>