Fix build on some linux distros.

The place where the PAGE_SIZE value is defined varies, mostly because
you're not supposed to be using it directly.  sysconf(_SC_PAGE_SIZE)
is the approved method, and in fact some Linux distros actually #define
PAGE_SIZE to the library call.
diff --git a/modules/gralloc/gralloc_priv.h b/modules/gralloc/gralloc_priv.h
index c3e34bd..aa757b1 100644
--- a/modules/gralloc/gralloc_priv.h
+++ b/modules/gralloc/gralloc_priv.h
@@ -18,7 +18,11 @@
 #define GRALLOC_PRIV_H_
 
 #include <stdint.h>
-#include <asm/page.h>
+#ifdef HAVE_ANDROID_OS      // just want PAGE_SIZE define
+# include <asm/page.h>
+#else
+# include <sys/user.h>
+#endif
 #include <limits.h>
 #include <sys/cdefs.h>
 #include <hardware/gralloc.h>