doc: add VFIO API in doxygen

Signed-off-by: Hemant Agrawal <hemant.agrawal@nxp.com>

doc/api/doxy-api-index.md

@@ -52,7 +52,8 @@ The public API headers are grouped by topics:
   [bitrate]            (@ref rte_bitrate.h),
   [latency]            (@ref rte_latencystats.h),
   [devargs]            (@ref rte_devargs.h),
-  [PCI]                (@ref rte_pci.h)
+  [PCI]                (@ref rte_pci.h),
+  [vfio]               (@ref rte_vfio.h)
 
 - **device specific**:
   [softnic]            (@ref rte_eth_softnic.h),

doc/api/doxy-api.conf

@@ -82,6 +82,7 @@ INPUT                   = doc/api/doxy-api-index.md \
 FILE_PATTERNS           = rte_*.h \
                           cmdline.h
 PREDEFINED              = __DOXYGEN__ \
+			   VFIO_PRESENT \
                           __attribute__(x)=
 
 OPTIMIZE_OUTPUT_FOR_C   = YES

lib/librte_eal/common/include/rte_vfio.h

@@ -5,6 +5,11 @@
 #ifndef _RTE_VFIO_H_
 #define _RTE_VFIO_H_
 
+/**
+ * @file
+ * RTE VFIO. This library provides various VFIO related utility functions.
+ */
+
 /*
  * determine if VFIO is present on the system
  */