gralloc: Use getpagesize() in place of PAGE_SIZE.

- Use getpagesize() function from unistd.h to get page size
  in place of PAGE_SIZE macro.
- Make isDisableUBWCForEncoder declaration pure virtual.

Change-Id: I89405e999e4683874f4daa32188181e688a19812
CRs-Fixed: 1069351
diff --git a/libgralloc/gr.h b/libgralloc/gr.h
index 578240a..5ab576a 100644
--- a/libgralloc/gr.h
+++ b/libgralloc/gr.h
@@ -24,6 +24,7 @@
 #include <hardware/gralloc.h>
 #include <pthread.h>
 #include <errno.h>
+#include <unistd.h>
 
 #include <cutils/native_handle.h>
 #include <utils/Singleton.h>
@@ -35,7 +36,7 @@
 struct private_handle_t;
 
 inline unsigned int roundUpToPageSize(unsigned int x) {
-    return (x + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1);
+    return (x + (getpagesize()-1)) & ~(getpagesize()-1);
 }
 
 template <class Type>