scripts/gdb/aarch64: add aarch64 page operation helper commands and configs

1. Move page table debugging from mm.py to pgtable.py.

2. Add aarch64 kernel config and memory constants value.

3. Add below aarch64 page operation helper commands.
   page_to_pfn, page_to_phys, pfn_to_page, page_address,
   virt_to_phys, sym_to_pfn, pfn_to_kaddr, virt_to_page.

4. Only support CONFIG_SPARSEMEM_VMEMMAP=y now.

Link: https://lkml.kernel.org/r/20230808083020.22254-5-Kuan-Ying.Lee@mediatek.com
Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Qun-Wei Lin <qun-wei.lin@mediatek.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>