docs: nfc: convert to ReST

Rename the nfc documentation files to ReST, add an
index for them and adjust in order to produce a nice html
output via the Sphinx build system.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/nfc/index.rst

+:orphan:
+
+========================
+Near Field Communication
+========================
+
+.. toctree::
+   :maxdepth: 1
+
+   nfc-hci
+   nfc-pn544

Documentation/nfc/nfc-pn544.txt → Documentation/nfc/nfc-pn544.rst

-Kernel driver for the NXP Semiconductors PN544 Near Field
-Communication chip
+============================================================================
+Kernel driver for the NXP Semiconductors PN544 Near Field Communication chip
+============================================================================
+
 
 General
 -------