linux/compat.h: port lower_32_bits and upper_32_bits from Linux

[backport from linux commit 204b885e and 218e180e7]
64 bit processors are becomming more and more popular.
lower_32_bits and upper_32_bits save our labor doing
shifts/manipulations like (u32)(n) and (u32)((n) >> 32).
They are good helpers in both little and big endian cases.
Port these two functions here from Linux:include/linux/kernel.h,
cater the comment message to little/big endian cases.
Later on, developers could include linux/compat.h if they want to
use these two functions.

Signed-off-by: Lijun Pan <Lijun.Pan@freescale.com>

include/linux/compat.h

@@ -57,4 +57,23 @@
 				  , __FILE__, __LINE__); }
 
 #define PAGE_SIZE	4096
+
+/**
+ * upper_32_bits - return MSB bits 32-63 of a number if little endian, or
+ * return MSB bits 0-31 of a number if big endian.
+ * @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))
+
+/**
+ * lower_32_bits - return LSB bits 0-31 of a number if little endian, or
+ * return LSB bits 32-63 of a number if big endian.
+ * @n: the number we're accessing
+ */
+#define lower_32_bits(n) ((u32)(n))
+
 #endif