add upper-32-bits macro

We keep on getting "right shift count >= width of type" warnings when doing
things like

	sector_t s;

	x = s >> 56;

because with CONFIG_LBD=n, s is only 32-bit.  Similar problems can occur with
dma_addr_t's.

So add a simple wrapper function which code can use to avoid this warning.
The above example would become

	x = upper_32_bits(s) >> 24;

The first user is in fact AFS.

Cc: James Bottomley <[email protected]>
Cc: "Cameron, Steve" <[email protected]>
Cc: "Miller, Mike (OS Dev)" <[email protected]>
Cc: Hisashi Hifumi <[email protected]>
Cc: Alan Cox <[email protected]>
Cc: David Howells <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/kernel.h

@@ -41,6 +41,16 @@ extern const char linux_proc_banner[];
 #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
 #define roundup(x, y) ((((x) + ((y) - 1)) / (y)) * (y))
 
+/**
+ * upper_32_bits - return bits 32-63 of a number
+ * @n: the number we're accessing
+ *
+ * A basic shift-right of a 64- or 32-bit quantity.  Use this to suppress
+ * the "right shift count >= width of type" warning when that quantity is
+ * 32-bits.
+ */
+#define upper_32_bits(n) ((u32)(((n) >> 16) >> 16))
+
 #define	KERN_EMERG	"<0>"	/* system is unusable			*/
 #define	KERN_ALERT	"<1>"	/* action must be taken immediately	*/
 #define	KERN_CRIT	"<2>"	/* critical conditions			*/