armv8/fsl-lsch3: Convert flushing L3 to assembly to avoid using stack

Flushing L3 cache in CCN-504 requries d-cache to be disabled. Using
assembly function to guarantee stack is not used before flushing is
completed. Timeout is needed for simualtor on which CCN-504 is not
implemented. Return value can be checked for timeout situation.

Change bootm.c to disable dcache instead of simply flushing, required
by flushing L3.

Signed-off-by: York Sun <yorksun@freescale.com>
diff --git a/arch/arm/cpu/armv8/cache.S b/arch/arm/cpu/armv8/cache.S
index 9c6e824..fa447bc 100644
--- a/arch/arm/cpu/armv8/cache.S
+++ b/arch/arm/cpu/armv8/cache.S
@@ -155,3 +155,9 @@
 	isb	sy
 	ret
 ENDPROC(__asm_invalidate_icache_all)
+
+ENTRY(__asm_flush_l3_cache)
+	mov	x0, #0			/* return status as success */
+	ret
+ENDPROC(__asm_flush_l3_cache)
+	.weak	__asm_flush_l3_cache