dt-bindings: riscv: add bfloat16 ISA extension description

Add description for the BFloat16 precision Floating-Point ISA extension,
(Zfbfmin, Zvfbfmin, Zvfbfwma). which was ratified in commit 4dc23d62
("Added Chapter title to BF16") of the riscv-isa-manual.

Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250213003849.147358-2-inochiama@gmail.com
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Author: inochisa

Documentation/devicetree/bindings/riscv/extensions.yaml

@@ -329,6 +329,12 @@ properties:
             instructions, as ratified in commit 056b6ff ("Zfa is ratified") of
             riscv-isa-manual.
 
+        - const: zfbfmin
+          description:
+            The standard Zfbfmin extension which provides minimal support for
+            16-bit half-precision brain floating-point instructions, as ratified
+            in commit 4dc23d62 ("Added Chapter title to BF16") of riscv-isa-manual.
+
         - const: zfh
           description:
             The standard Zfh extension for 16-bit half-precision binary
@@ -525,6 +531,18 @@ properties:
             in commit 6f702a2 ("Vector extensions are now ratified") of
             riscv-v-spec.
 
+        - const: zvfbfmin
+          description:
+            The standard Zvfbfmin extension for minimal support for vectored
+            16-bit half-precision brain floating-point instructions, as ratified
+            in commit 4dc23d62 ("Added Chapter title to BF16") of riscv-isa-manual.
+
+        - const: zvfbfwma
+          description:
+            The standard Zvfbfwma extension for vectored half-precision brain
+            floating-point widening multiply-accumulate instructions, as ratified
+            in commit 4dc23d62 ("Added Chapter title to BF16") of riscv-isa-manual.
+
         - const: zvfh
           description:
             The standard Zvfh extension for vectored half-precision
@@ -663,6 +681,33 @@ properties:
         then:
           contains:
             const: zca
+      # Zfbfmin depends on F
+      - if:
+          contains:
+            const: zfbfmin
+        then:
+          contains:
+            const: f
+      # Zvfbfmin depends on V or Zve32f
+      - if:
+          contains:
+            const: zvfbfmin
+        then:
+          oneOf:
+            - contains:
+                const: v
+            - contains:
+                const: zve32f
+      # Zvfbfwma depends on Zfbfmin and Zvfbfmin
+      - if:
+          contains:
+            const: zvfbfwma
+        then:
+          allOf:
+            - contains:
+                const: zfbfmin
+            - contains:
+                const: zvfbfmin
 
 allOf:
   # Zcf extension does not exist on rv64