doc: board: apple: Mention M1 Ultra support

U-Boot now supports the M1 Ultra SoC as found in the new Mac Studio.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
diff --git a/doc/board/apple/m1.rst b/doc/board/apple/m1.rst
index 083bfb0..8fa7637 100644
--- a/doc/board/apple/m1.rst
+++ b/doc/board/apple/m1.rst
@@ -10,6 +10,7 @@
  - Apple M1 SoC (t8103)
  - Apple M1 Pro SoC (t6000)
  - Apple M1 Max SoC (t6001)
+ - Apple M1 Ultra SoC (t6002)
 
 On these SoCs the following hardware is supported:
 
@@ -78,5 +79,5 @@
      - Base Address
    * - M1 (t8103)
      - 0x235200000
-   * - M1 Pro/Max (t6000/t6001)
+   * - M1 Pro/Max/Ultra (t6000/t6001/t6002)
      - 0x39b200000