scripts/checkstack.pl: dynamic stack growth for aarch64

scripts/checkstack.pl: dynamic stack growth for aarch64

This is to track dynamic amount of stack growth for aarch64, so it is
possible to print out offensive functions that may consume too much stack.
For example,

0xffff2000084d1270 try_to_unmap_one [vmlinux]:		Dynamic (0xcf0)
0xffff200008538358 migrate_page_move_mapping [vmlinux]:	Dynamic (0xc60)
0xffff2000081276c8 copy_process.isra.2 [vmlinux]:	Dynamic (0xb20)
0xffff200008424958 show_free_areas [vmlinux]:		Dynamic (0xb40)
0xffff200008545178 __split_huge_pmd_locked [vmlinux]:	Dynamic (0xb30)
0xffff200008555120 collapse_shmem [vmlinux]:		Dynamic (0xbc0)
0xffff20000862e0d0 do_direct_IO [vmlinux]:		Dynamic (0xb70)
0xffff200008cc0aa0 md_do_sync [vmlinux]:		Dynamic (0xb90)

Link: http://lkml.kernel.org/r/20181208025143.39363-1-cai@lca.pw
Signed-off-by: Qian Cai <cai@lca.pw>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>