docs: mmc: move it to the driver-api

Most of the stuff here is related to the kAPI.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/driver-api/mmc/index.rst

@@ -0,0 +1,11 @@
+========================
+MMC/SD/SDIO card support
+========================
+
+.. toctree::
+   :maxdepth: 1
+
+   mmc-dev-attrs
+   mmc-dev-parts
+   mmc-async-req
+   mmc-tools