mmc: sdhci-iproc: remove hard coded mmc cap 1.8v

Remove hard coded mmc cap 1.8v from platform data as it is board specific.
The 1.8v DDR mmc caps can be enabled using DTS property for those
boards that support it.

Fixes: b17b4ab8

 ("mmc: sdhci-iproc: define MMC caps in platform data")
Signed-off-by: Srinath Mannam <srinath.mannam@broadcom.com>
Signed-off-by: Scott Branden <scott.branden@broadcom.com>
Reviewed-by: Ray Jui <ray.jui@broadcom.com>
Cc: stable@vger.kernel.org # v4.8+
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>