drm: remove drm_public macro

Some compilers (like the Oracle Studio), require that the function
declaration must be annotated with the same visibility attribute as the
definition. As annotating functions with drm_public is no longer
required just remove the macro.

Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Damien Lespiau <damien.lespiau@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Cc: Michel Dänzer <michel.daenzer@amd.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
diff --git a/configure.ac b/configure.ac
index c25a813..e715262 100644
--- a/configure.ac
+++ b/configure.ac
@@ -403,14 +403,13 @@
 	    [kernel_source="$with_kernel_source"])
 AC_SUBST(kernel_source)
 
-AC_MSG_CHECKING([whether $CC supports __attribute__((visibility))])
+AC_MSG_CHECKING([whether $CC supports __attribute__(("hidden"))])
 AC_LINK_IFELSE([AC_LANG_PROGRAM([
-    int foo_default( void ) __attribute__((visibility("default")));
     int foo_hidden( void ) __attribute__((visibility("hidden")));
 ])], HAVE_ATTRIBUTE_VISIBILITY="yes"; AC_MSG_RESULT([yes]), AC_MSG_RESULT([no]));
 
 if test "x$HAVE_ATTRIBUTE_VISIBILITY" = xyes; then
-    AC_DEFINE(HAVE_VISIBILITY, 1, [Compiler supports __attribute__((visibility))])
+    AC_DEFINE(HAVE_VISIBILITY, 1, [Compiler supports __attribute__(("hidden"))])
 fi
 
 AC_SUBST(WARN_CFLAGS)