Add device tree binding documentation for the Black Sesame Technologies
(BST) DWCMSHC SDHCI controller.

This binding describes the required and optional properties for the
bst,dwcmshc-sdhci compatible controller, including register layout,
interrupts, bus width, clock configuration, and other controller-specific
features.

---
Changes for v2:
- Simplified description, removed redundant paragraphs
- Updated $schema to reference mmc-specific scheme
- Corrected compatible to add soc name
(bst,c1200-dwcmshc-sdhci)
- Removed all redundant property descriptions
- Dropped invalid mmc_crm_base/size properties, use reg for all address
ranges
- Cleaned up required properties to only essential entries
- Standardized example DTS format, fixed reg syntax and property
ordering
- Removed additionalProperties: true

Signed-off-by: Ge Gordon <gordon.ge@bst.ai>
Signed-off-by: Albert Yang <redacted>
---
 .../bindings/mmc/bst,dwcmshc-sdhci.yaml       | 67 +++++++++++++++++++
 1 file changed, 67 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mmc/bst,dwcmshc-sdhci.yaml

diff --git a/Documentation/devicetree/bindings/mmc/bst,dwcmshc-sdhci.yaml b/Documentation/devicetree/bindings/mmc/bst,dwcmshc-sdhci.yaml
new file mode 100644
index 000000000000..699dc404caac
--- /dev/null
+++ b/Documentation/devicetree/bindings/mmc/bst,dwcmshc-sdhci.yaml

@@ -0,0 +1,67 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mmc/bst,dwcmshc-sdhci.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Black Sesame Technologies DWCMSHC SDHCI Controller
+
+maintainers:
+  - Ge Gordon <gordon.ge@bst.ai>
+
+allOf:
+  - $ref: mmc-controller.yaml#
+
+properties:
+  compatible:
+    const: bst,c1200-dwcmshc-sdhci
+
+  reg:
+    maxItems: 2
+    description: |
+      Register base addresses and sizes for the SDHCI controller.
+      First entry is the core SDHCI registers, second entry is the
+      CRM registers.