board: asus: grouper: implement multi-DTB support

Use board revision detection mechanism to choose correct DTB.
Adjust documentation and build setup accordingly.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
diff --git a/doc/board/asus/grouper_common.rst b/doc/board/asus/grouper.rst
similarity index 93%
rename from doc/board/asus/grouper_common.rst
rename to doc/board/asus/grouper.rst
index 47a854e..d56a9ca 100644
--- a/doc/board/asus/grouper_common.rst
+++ b/doc/board/asus/grouper.rst
@@ -19,14 +19,14 @@
 Build U-Boot
 ------------
 
-Device support is implemented by applying config fragment to a generic board
-defconfig. Valid fragments are ``tilapia.config``, ``grouper_E1565.config``
-and ``grouper_PM269.config``.
+U-Boot features ability to detect grouper board revision on which it is
+loaded. Currently are supported both TI and MAXIM based WiFi-only models
+along with cellular one.
 
 .. code-block:: bash
 
     $ export CROSS_COMPILE=arm-linux-gnueabi-
-    $ make grouper_common_defconfig grouper_E1565.config # For maxim based grouper
+    $ make grouper_defconfig # For all grouper versions and tilapia
     $ make
 
 After the build succeeds, you will obtain the final ``u-boot-dtb-tegra.bin``
diff --git a/doc/board/asus/index.rst b/doc/board/asus/index.rst
index 2b10328..2cac04c 100644
--- a/doc/board/asus/index.rst
+++ b/doc/board/asus/index.rst
@@ -6,6 +6,6 @@
 .. toctree::
    :maxdepth: 2
 
-   grouper_common
+   grouper
    transformer_t20
    transformer_t30