Update documentation by pointing out that it's applicable mostly
for a legacy platform. While at it, add couple of points with regard
to ACPI, Device Tree, and automatic DMA enablement.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210517140351.901-9-andriy.shevchenko@linux.intel.comSigned-off-by: NMark Brown <broonie@kernel.org>