mmc: sdhci: add adma_table_cnt member to struct sdhci_host

This patch adds adma_table_cnt member to struct sdhci_host to give more
flexibility to drivers to control the ADMA table count.

Default value of adma_table_cnt is set to (SDHCI_MAX_SEGS * 2 + 1).

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>