scsi: dt-bindings: ufs: Fix the compatible string definition

If you look at the bindings for the UFS Host Controller it says:

- compatible: must contain "jedec,ufs-1.1" or "jedec,ufs-2.0", may
              also list one or more of the following:
                 "qcom,msm8994-ufshc"
                 "qcom,msm8996-ufshc"
                 "qcom,ufshc"

My reading of that is that it's fine to just have either of these:
1. "qcom,msm8996-ufshc", "jedec,ufs-2.0"
2. "qcom,ufshc", "jedec,ufs-2.0"

As far as I can tell neither of the above is actually a good idea.

For #1 it turns out that the driver currently only keys off the
compatible string "qcom,ufshc" so it won't actually probe.

For #2 the driver won't probe but it's not a good idea to keep the SoC
name out of the compatible string.

Let's update the compatible string to make it really explicit.  We'll
include a nod to the existing driver and the old binding and say that
we should always include the "qcom,ufshc" string in addition to the
SoC compatible string.

While we're at it we'll also include another example SoC known to have
UFS: sdm845.

Fixes: 47555a5c ("scsi: ufs: make the UFS variant a platform device")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt

@@ -4,11 +4,14 @@ UFSHC nodes are defined to describe on-chip UFS host controllers.
 Each UFS controller instance should have its own node.
 
 Required properties:
-- compatible		: must contain "jedec,ufs-1.1" or "jedec,ufs-2.0", may
-			  also list one or more of the following:
-					  "qcom,msm8994-ufshc"
-					  "qcom,msm8996-ufshc"
-					  "qcom,ufshc"
+- compatible		: must contain "jedec,ufs-1.1" or "jedec,ufs-2.0"
+
+			  For Qualcomm SoCs must contain, as below, an
+			  SoC-specific compatible along with "qcom,ufshc" and
+			  the appropriate jedec string:
+			    "qcom,msm8994-ufshc", "qcom,ufshc", "jedec,ufs-2.0"
+			    "qcom,msm8996-ufshc", "qcom,ufshc", "jedec,ufs-2.0"
+			    "qcom,sdm845-ufshc", "qcom,ufshc", "jedec,ufs-2.0"
 - interrupts        : <interrupt mapping for UFS host controller IRQ>
 - reg               : <registers mapping>