mmc: sdhci: Allow platform controlled voltage switching

mmc: sdhci: Allow platform controlled voltage switching

If vendor platform drivers are controlling whole logic of voltage
switching, then sdhci driver no need control vqmmc regulator.
So skip enabling/disable vqmmc from SDHC driver.

Signed-off-by: Vijay Viswanath <vviswana@codeaurora.org>
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/1592919288-1020-2-git-send-email-vbadigan@codeaurora.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>