mmc: renesas_sdhi_internal_dmac: limit DMA RX for old SoCs

Early revisions of certain SoCs cannot do multiple DMA RX streams in
parallel. To avoid data corruption, only allow one DMA RX channel and
fall back to PIO, if needed.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Nguyen Viet Dung <dung.nguyen.aj@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>