ANDROID: scsi: ufs: allow ufs variants to override sg entry size

Modify the UFSHCD core to allow 'struct ufshcd_sg_entry' to be
variable-length.  The default is the standard length, but variants can
override ufs_hba::sg_entry_size with a larger value if there are
vendor-specific fields following the standard ones.

This is needed to support inline encryption with ufs-exynos (FMP).

Bug: 129991660
Change-Id: I6ab9458d5c23331013e6b736d6fea378a6b5b86c
Signed-off-by: Eric Biggers <ebiggers@google.com>