doc: driver-model: Convert pci-info.txt to reST

Convert plain text documentation to reStructuredText format and add
it to Sphinx TOC tree. No essential content change.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/doc/driver-model/index.rst b/doc/driver-model/index.rst
index d1c19a4..a83c648 100644
--- a/doc/driver-model/index.rst
+++ b/doc/driver-model/index.rst
@@ -13,3 +13,4 @@
    livetree
    migration
    of-plat
+   pci-info