Fixed std::isfinite vs isfinite differences

Added PX4_ISFINITE(x) to px4_defines.h to handle the differences on
NuttX and Linux.

This change also picked up some file renaming for virtual character devices

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/platforms/px4_defines.h

@@ -104,6 +104,8 @@ typedef param_t px4_param_t;
 
 #define px4_statfs_buf_f_bavail_t int
 
+#define PX4_ISFINITE(x) isfinite(x)
+
 /* Linux Specific defines */
 #elif defined(__PX4_LINUX)
 
@@ -165,6 +167,8 @@ __END_DECLS
 #define M_DEG_TO_RAD 		0.01745329251994
 #define M_RAD_TO_DEG 		57.2957795130823
 
+#define PX4_ISFINITE(x) std::isfinite(x)
+
 #endif
 
 /* Defines for all platforms */