pylibfdt: Don't have setup.py depend on where it's invoked from

Currently setup.py depends on being invoked from the right directory
(specifically it needs to be run from the root of the project).  That's a
bit confusing.

This updates setup.py to no longer depend on the invoking directory by
instead having it change directory to the location of the script itself,
then using internal paths relative to that.

Signed-off-by: David Gibson <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
diff --git a/pylibfdt/libfdt.i b/pylibfdt/libfdt.i
index 842e7b6..462b5b0 100644
--- a/pylibfdt/libfdt.i
+++ b/pylibfdt/libfdt.i
@@ -1028,7 +1028,7 @@
  */
 typedef uint32_t fdt32_t;
 
-%include "libfdt/fdt.h"
+%include "fdt.h"
 
 %include "typemaps.i"
 
@@ -1134,4 +1134,4 @@
  */
 int fdt_property_stub(void *fdt, const char *name, const char *val, int len);
 
-%include <../libfdt/libfdt.h>
+%include <libfdt.h>