scsi: ufs: make the UFS variant a platform device

scsi: ufs: make the UFS variant a platform device

This change turns the UFS variant (SCSI_UFS_QCOM) into a UFS
a platform device.
In order to do so a few additional changes are required:
1. The ufshcd-pltfrm is no longer serves as a platform device.
   Now it only serves as a group of platform APIs such as PM APIs
   (runtime suspend/resume, system suspend/resume etc), parsers of
   clocks, regulators and pm_levels from DT.
2. What used to be the old platform "probe" is now "only"
   a pltfrm_init() routine, that does exactly the same, but only
   being called by the new probe function of the UFS variant.

Reviewed-by: Rob Herring <robherring2@gmail.com>
Reviewed-by: Gilad Broner <gbroner@codeaurora.org>
Signed-off-by: Yaniv Gardi <ygardi@codeaurora.org>
Tested-by: Alim Akhtar <alim.akhtar@samsung.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>