mmc: sdhci: Add new callback to enable/disable CDR

MSM SDHCI has CDR mechanism (clock-data recovery) to
automatically adjust the sampling point based on the
voltage/temperature variations. This must be enabled
for only read. Hence, add new host op toggle_cdr to
control CDR.

Change-Id: I75940cfca15fe88de6d46fe58cb33620a3b7ced1
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>