mmc: debugfs: implement ios show for SDR12 and SDR25

This patch add MMC_TIMING_UHS_SDR12 and MMC_TIMING_UHS_SDR25
for mmc_ios_show to show the ios->timing if mmc card runs under
these two modes.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>