On the Amlogic G12A SoC family, (only) the SDIO controller fails to access
the data from DRAM, leading to a broken controller.

But each MMC controller has 1,5KiB of SRAM after the registers, that can
be used as bounce buffer to avoid direct DRAM access from the integrated
DMAs (this SRAM may be used by the boot ROM when DRAM is not yet initialized).

The quirk is to disable the chained descriptor for this controller, and
use this SRAM memory zone as buffer for the bounce buffer fallback mode.

The performance hit hasn't been evaluated, but the fix has been tested
using a WiFi AP6398S SDIO module, and the iperf3 Bandwidth measurement gave
55.2 Mbits/sec over a 63 Hours long test, with the SDIO ios set as High-Speed
at 50MHz clock. It gave 170 Mbits/sec as SDR104 and 200MHz clock.
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Guillaume La Roque <glaroque@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>