[BUG] ARM64: Create 4K page size mmu memory map at init time will trigger exception.

["Leizhen (ThunderTown, Euler)" <thunder.leizhen@huawei.com>]

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This problem is on ARM64. When CONFIG_ARM64_64K_PAGES is not opened, the memory map size can be 2M(section) and 4K(PAGE). First, OS will create map for pgd(level 1 table) and level 2 table which in swapper_pg_dir. Then, OS register mem block into memblock.memory according to memory node in fdt, like memory@0, and create map in setup_arch-->paging_init. If all mem block start address and size is integral multiple of 2M, there is no problem, because we will create 2M section size map whose entries locate in level 2 table. But if it is not integral multiple of 2M, we should create level 3 table, which granule is 4K. Now, current implementtion is call early_alloc-->memblock_alloc to alloc memory for level 3 table. This function will find a 4K free memory which locate in memblock.memory tail(high address), but paging_init is create map from low address to high address, so new alloced memory is not mapped, write page talbe entry to it will trigger exception.

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