arm64: asm: add CPU_LE & CPU_BE assembler helpers

Add CPU_LE and CPU_BE to select assembler code in little and big
endian configurations respectively.
Signed-off-by: Matthew Leach <matthew.leach@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/assembler.h

@@ -115,6 +115,25 @@ lr	.req	x30		// link register
 	.align	7
 	b	\label
 	.endm
+
+/*
+ * Select code when configured for BE.
+ */
+#ifdef CONFIG_CPU_BIG_ENDIAN
+#define CPU_BE(code...) code
+#else
+#define CPU_BE(code...)
+#endif
+
+/*
+ * Select code when configured for LE.
+ */
+#ifdef CONFIG_CPU_BIG_ENDIAN
+#define CPU_LE(code...)
+#else
+#define CPU_LE(code...) code
+#endif
+
 /*
  * Define a macro that constructs a 64-bit value by concatenating two
  * 32-bit registers. Note that on big endian systems the order of the