mmc: sdhci-pltfm: Drop define for SDHCI_PLTFM_PMOPS

Due to previous changes this define has no longer a purpose. Instead move
the sdhci-pltfm drivers over to use the exported struct sdhci_pltfm_pmops.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>