Move val_prettyformat to valprint.h

I stumbled across an ancient FIXME comment that was easy to fix --
val_prettyformat does not need to be in defs.h, and is easily moved to
valprint.h, where (despite what the comment says) it belongs.

Tested by rebuilding.

gdb/defs.h

diff --git a/gdb/defs.h b/gdb/defs.h
index 454475b..f5af3e6 100644
--- a/gdb/defs.h
+++ b/gdb/defs.h
@@ -410,20 +410,6 @@ enum info_proc_what
 extern unsigned input_radix;
 extern unsigned output_radix;
 
-/* * Possibilities for prettyformat parameters to routines which print
-   things.  Like enum language, this should be in value.h, but needs
-   to be here for the same reason.  FIXME:  If we can eliminate this
-   as an arg to LA_VAL_PRINT, then we can probably move it back to
-   value.h.  */
-
-enum val_prettyformat
-  {
-    Val_no_prettyformat = 0,
-    Val_prettyformat,
-    /* * Use the default setting which the user has specified.  */
-    Val_prettyformat_default
-  };
-
 /* * Optional native machine support.  Non-native (and possibly pure
    multi-arch) targets do not need a "nm.h" file.  This will be a
    symlink to one of the nm-*.h files, built by the `configure'

gdb/valprint.h

diff --git a/gdb/valprint.h b/gdb/valprint.h
index cf5e2f2..0a88780 100644
--- a/gdb/valprint.h
+++ b/gdb/valprint.h
@@ -22,6 +22,17 @@
 
 #include "cli/cli-option.h"
 
+/* Possibilities for prettyformat parameters to routines which print
+   things.  */
+
+enum val_prettyformat
+  {
+    Val_no_prettyformat = 0,
+    Val_prettyformat,
+    /* * Use the default setting which the user has specified.  */
+    Val_prettyformat_default
+  };
+
 /* This is used to pass formatting options to various value-printing
    functions.  */
 struct value_print_options