ANDROID: ufs: Enable CONFIG_SCSI_UFS_VARIABLE_SG_ENTRY_SIZE

Since the Exynos UFS host controller driver is supported by the GKI
kernel, CONFIG_SCSI_UFS_VARIABLE_SG_ENTRY_SIZE needs to be enabled.
This CL is necessary because the Pixel 6/7 Exynos UFS host controller
driver is not upstream and because the kernel configuration symbol that
controls whether or not that driver is built is not present in the
upstream kernel either (CONFIG_SCSI_UFS_EXYNOS_GS).

Bug: 271162672
Change-Id: Ib74f2c2638b8de272edfb2b2e4d2d9f006468e51
Signed-off-by: Robin Peng <robinpeng@google.com>
[ bvanassche: modified CL title and rewrote CL description ]
Signed-off-by: Bart Van Assche <bvanassche@google.com>