doc: Add new doc for soc ID driver model

Add a new documentation file for UCLASS_SOC and its usage to describe
the SoC Device ID framework that allows SoC identification and device
data matching.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/driver-model/index.rst b/doc/driver-model/index.rst
index b9df221..f17c72c 100644
--- a/doc/driver-model/index.rst
+++ b/doc/driver-model/index.rst
@@ -19,5 +19,6 @@
    pmic-framework
    remoteproc-framework
    serial-howto
+   soc-framework
    spi-howto
    usb-info