linux/kernel.h: import DIV_ROUND_CLOSEST_ULL from Linux

Copied from Linux v4.20-rc7.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

include/linux/kernel.h

@@ -102,6 +102,18 @@
 		(((__x) - ((__d) / 2)) / (__d));	\
 }							\
 )
+/*
+ * Same as above but for u64 dividends. divisor must be a 32-bit
+ * number.
+ */
+#define DIV_ROUND_CLOSEST_ULL(x, divisor)(		\
+{							\
+	typeof(divisor) __d = divisor;			\
+	unsigned long long _tmp = (x) + (__d) / 2;	\
+	do_div(_tmp, __d);				\
+	_tmp;						\
+}							\
+)
 
 /*
  * Multiplies an integer by a fraction, while avoiding unnecessary