drivers: flash: stm32h7x: handle ECC errors on read

The STM32H7x flash has an integrated ECC that can correct single
errors and detect double errors. When a double ECC error is detected,
the DBECCERR1/2 flag is raised and there is a bus fault.

We now mask this bus fault and check the error flags. ECC errors are
logged with the offset of the data. Single ECC errors cause a warning
to be logged and double ECC errors return -EIO.

Fixes #33140.

Signed-off-by: Göran Weinholt <goran.weinholt@endian.se>