scsi: ufs: core: Convert string descriptor format macros to enum

scsi: ufs: core: Convert string descriptor format macros to enum

Convert SD_ASCII_STD and SD_RAW from boolean macros to enum values for
improved code readability. This makes ufshcd_read_string_desc() calls
self-documenting by using explicit enum values instead of true/false.

Move the ufshcd_read_string_desc() declaration from include/ufs/ufshcd.h
to drivers/ufs/core/ufshcd-priv.h since this function is not exported.

Co-developed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Suggested-by: Avri Altman <Avri.Altman@sandisk.com>
Signed-off-by: Bean Huo <beanhuo@micron.com>
Link: https://patch.msgid.link/20251107230518.4060231-2-beanhuo@iokpp.de
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>