armv8: mmu: Add a function to change mapping attributes

Function mmu_change_region_attr() is added to change existing mapping
with updated PXN, UXN and memory type. This is a break-before-make
process during which the mapping becomes fault (invalid) before final
attributres are set.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/arm/include/asm/system.h b/arch/arm/include/asm/system.h
index 766e929..9c3261c 100644
--- a/arch/arm/include/asm/system.h
+++ b/arch/arm/include/asm/system.h
@@ -226,6 +226,7 @@
 void smp_kick_all_cpus(void);
 
 void flush_l3_cache(void);
+void mmu_change_region_attr(phys_addr_t start, size_t size, u64 attrs);
 
 /*
  *Issue a secure monitor call in accordance with ARM "SMC Calling convention",