iio: accel: st_sensors: Support generic mounting matrix

The ST accelerators support a special type of quirky mounting matrix found
in ACPI systems, but not a generic mounting matrix such as from the device
tree.

Augment the ACPI hack to be a bit more generic and accept a mounting
matrix from device properties.

This makes it possible to fix orientation on the Ux500 HREF device.

Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Denis Ciocca <denis.ciocca@st.com>
Cc: Daniel Drake <drake@endlessm.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20210518230722.522446-2-linus.walleij@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>