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>

arch/arm/include/asm/system.h

@@ -70,6 +70,7 @@ void __asm_invalidate_dcache_all(void);
 void __asm_flush_dcache_range(u64 start, u64 end);
 void __asm_invalidate_tlb_all(void);
 void __asm_invalidate_icache_all(void);
+int __asm_flush_l3_cache(void);
 
 void armv8_switch_to_el2(void);
 void armv8_switch_to_el1(void);