mmc: sdhci-msm: Implement platform_execute_tuning and toggle_cdr callbacks

Implement platform_execute_tuning and toggle_cdr callbacks that are
needed to support HS200 and SDR104 bus speed modes. Also, set
IO_PAD_PWR_SWITCH control bit in vendor specific register if
the IO voltage level is within low voltage range (1.7v - 1.9v).

Change-Id: If41704758d097229ffc0204d581886e137e8b581
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
[xiaonian@codeaurora.org: fix trivial merge conflict]
Signed-off-by: Xiaonian Wang <xiaonian@codeaurora.org>