mmc: sdhci: add sdma_boundary member to struct sdhci_host

This patch adds sdma_boundary member to struct sdhci_host to give more
flexibility to drivers to control the sdma boundary buffer value and
also to fix issue on some sdhci controllers which are broken when
HOST SDMA Buffer Boundary is programmed in Block Size Register (0x04)
when using ADMA. Qualcomm sdhci controller is one of such type, writing
to this bits is un-supported.

Default value of sdma_boundary is set to SDHCI_DEFAULT_BOUNDARY_ARG.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>