mmc:sdhci-bayhub:provide a solution to improve sd host card compatibi…

…lity

Improve the signal integrity for long SD bus trace with GGC SD host redriver chip
1.GGC is a SD bus signal re-timing IC that has been paired with the SC7180 sometimes.
2.The key points as below:
 2.1 GGC chip is initialized during SD initialization
 2.2 GGC special tuning flow is used to re-timing SD bus signal.
 2.3 GGC power signal control should follow sd host power signal control.
3.The function of the patch is already verified on Chrome OS, and Google request us to submit the patch to Linux for them future use.
4.GGC can work with any other standard SDHCI controller to improve SD signal SI and Timing.
5.GGC has cooperated with Intel/Qualcomm/MTK/SPRD sd host already and work well.
6.This file is created for collecting the GGC chip support APIs and variables
This patch depends on patch:
mmc:sdhci-msm:fix Qualcomm sd host 7180 SD card compatibility issue

Signed-off-by: Chevron Li <chevron.li@bayhubtech.com>