Update dump-syscalls.sh to generate 32-bit syscalls for aarch64

Update dump-syscalls.sh to generate 32-bit syscalls for aarch64

The aarch64 kernel can support aarch32 syscalls when CONFIG_COMPAT is set
in the kernel configuration (https://cateee.net/lkddb/web-lkddb/COMPAT.html).
This is set on the the aarch64 Fedora 29 kernels and causes builds to
fail with:

OUT semantic error: unresolved arity-1 global array __syscall_32_num2name, missing global declaration?: identifier '__syscall_32_num2name' at /usr/share/systemtap/tapset/linux/syscall_table.stp:8:16
        source:         return __syscall_32_num2name[num]
                               ^

Pass 2: analysis failed.  [man error::pass2]

Adding generation of the 32-bit syscall information for aarch64 to
address this.