svm: fix asan check failed @svm_map_region on arm

==283032==AddressSanitizer CHECK failed: compiler-rt/lib/asan/asan_mapping.h:366
          "((AddrIsInMem(p))) != (0)" (0x0, 0x0)
    #0 0x49c128 in __asan::AsanCheckFailed
    #1 0x4ae8dc in __sanitizer::CheckFailed
    #2 0x495dec in __asan::ShadowSegmentEndpoint::ShadowSegmentEndpoint
    #3 0x495e48 in __asan_unpoison_memory_region
    #4 0xfffff4e851f8 in svm_map_region /home/vpp/src/svm/svm.c:611:7
    #5 0xfffff4e86d9c in svm_region_init_internal /home/vpp/src/svm/svm.c:797:8
    #6 0xfffff4e87ce4 in svm_region_init_args /home/vpp/src/svm/svm.c:880:3
    #7 0xfffff7f30d30 in vlibmemory_init /home/vpp/src/vlibmemory/memory_api.c:974:3
    #8 0xfffff4fd5368 in vlib_main /home/vpp/src/vlib/main.c:1986:16

svm_global_region_base_va 0x200000000000 is not in the aarch64 mapping range,
leading check failure and vpp cannot start.

aarch64 asan mapping
|| `[0x201000000000, 0xffffffffffff]` || HighMem    ||
|| `[0x041200000000, 0x200fffffffff]` || HighShadow ||
|| `[0x001200000000, 0x0411ffffffff]` || ShadowGap  ||
|| `[0x001000000000, 0x0011ffffffff]` || LowShadow  ||
|| `[0x000000000000, 0x000fffffffff]` || LowMem     ||

x86 asan mapping
|| `[0x10007fff8000, 0x7fffffffffff]` || HighMem    ||
|| `[0x02008fff7000, 0x10007fff7fff]` || HighShadow ||
|| `[0x00008fff7000, 0x02008fff6fff]` || ShadowGap  ||
|| `[0x00007fff8000, 0x00008fff6fff]` || LowShadow  ||
|| `[0x000000000000, 0x00007fff7fff]` || LowMem     ||

Type: fix

Signed-off-by: Tianyu Li <tianyu.li@arm.com>
Change-Id: I55ddbdcd361d66d4cfaf6459b2fa20fd8b64af37