mmc: sdhci-pci: Let suspend/resume callbacks replace default callbacks

The suspend / resume callbacks lack the flexibility to allow a device to
specify a different function entirely. Change them around so that device
functions are called directly and they in turn can call the default
implementations if needed.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Ludovic Desroches <ludovic.desroches@microchip.com>