scsi: ufs: add ufshcd_get_variant ufshcd_set_variant

This patch adds ufshcd_get_variant() and ufshcd_set_variant()
routines in order to get/set the variant specific data.

Reviewed-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Subhash Jadavani <subhashj@codeaurora.org>
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>