mmc: core: fix init controller performance regression, updated patch

Add MMC_CAP2_NO_PRESCAN_POWERUP to sdhci-pci.c also, use mmc_power_off()
for MMC_CAP2_NO_PRESCAN_POWERUP.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
[cjb: previously applied v1 of this patch instead of v4]
Signed-off-by: Chris Ball <cjb@laptop.org>