OMAPDSS: move the creation of debugfs files

Instead of having an ugly #ifdef mess in the core.c for creating debugfs
files, add a dss_debugfs_create_file() function that the dss drivers
can use to create the debugfs files.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/drivers/video/omap2/dss/rfbi.c b/drivers/video/omap2/dss/rfbi.c
index c5e6906..6adbea9 100644
--- a/drivers/video/omap2/dss/rfbi.c
+++ b/drivers/video/omap2/dss/rfbi.c
@@ -819,7 +819,7 @@
 }
 EXPORT_SYMBOL(omap_rfbi_update);
 
-void rfbi_dump_regs(struct seq_file *s)
+static void rfbi_dump_regs(struct seq_file *s)
 {
 #define DUMPREG(r) seq_printf(s, "%-35s %08x\n", #r, rfbi_read_reg(r))
 
@@ -976,6 +976,8 @@
 
 	rfbi_runtime_put();
 
+	dss_debugfs_create_file("rfbi", rfbi_dump_regs);
+
 	return 0;
 
 err_runtime_get: