stand/libofw: make OF_hasprop() part of the library

Currently it is only needed by powerpc ofwfdt.c, and defined statically
there. Make it available as part of libofw, mirroring what we have in
the kernel.

Two small tweaks are made to the implementation:
  1. Return type is changed to bool
  2. Return 'true' when OF_getproplen() == 0. This matches the expected
     semantics of the kernel version, described in OF_hasprop(9).

Reviewed by:	manu, imp, adrian
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D56429

stand/libofw/openfirm.c

@@ -288,6 +288,13 @@ OF_getencprop(phandle_t package, const char *propname, cell_t *buf, int buflen)
 	return (retval);
 }
 
+/* Check existence of a property of a package. */
+bool
+OF_hasprop(phandle_t node, const char *prop)
+{
+	return (OF_getproplen(node, prop) >= 0);
+}
+
 /* Get the next property of a package. */
 int
 OF_nextprop(phandle_t package, const char *previous, char *buf)

stand/libofw/openfirm.h

@@ -89,6 +89,7 @@ phandle_t	OF_instance_to_package(ihandle_t);
 int		OF_getproplen(phandle_t, const char *);
 int		OF_getprop(phandle_t, const char *, void *, int);
 int		OF_getencprop(phandle_t, const char *, cell_t *, int);
+bool		OF_hasprop(phandle_t, const char *);
 int		OF_nextprop(phandle_t, const char *, char *);
 int		OF_setprop(phandle_t, const char *, void *, int);
 int		OF_canon(const char *, char *, int);

stand/powerpc/ofw/ofwfdt.c

@@ -32,12 +32,6 @@
 
 extern int command_fdt_internal(int argc, char *argv[]);
 
-static int
-OF_hasprop(phandle_t node, const char *prop)
-{
-	return (OF_getproplen(node, (char *)prop) > 0);
-}
-
 static void
 add_node_to_fdt(void *buffer, phandle_t node, int fdt_offset)
 {