mfd: rtsx: Implement driving adjustment to device-dependent callbacks

Implement different ways of selecting driving capability(a necessary adjustment
along with voltage change). It was origionally in device-independent
mmc/host/rtsx_pci_sdmmc.c. Moving it here to support devices which may have a
different way of adjustment.

Signed-off-by: Roger Tseng <rogerable@realtek.com>
Reviewed-by: Wei WANG <wei_wang@realsil.com.cn>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>