Fix memory displacement overflowing i32 on AArch64

[charleywright]

For AArch64 instructions like 'LDR Xn, #imm' at addresses larger than i32::MAX the displacement overflows, producing an incorrect value. Fixed by returning i64 directly, as capstone does.

I ran into this with the following code:

__stubs:0000000100007324 50 1b 00 58         LDR     X16, #0x10000768C
__stubs:0000000100007328 00 02 1F D6         BR      X16

Without this change 0x10000768C overflows i32, giving a displacement of 0x768c.

I created a second branch for testing which adds an extra log in cstool - capstone-v6-test, that allows running this command:

cargo run --bin cstool -- --arch aarch64 --mode arm --detail --addr 100007324 --code "501b0058"
 100007324:  50 1b 00 58                         ldr     x16, 0x10000768c
             insn id:     634
             read regs:
             write regs:  x16
             insn groups:
offset: 0x10000768c

This matches the output of capstone's cstool:

./cstool -d aarch64 501b0058 0x100007324
100007324  50 1b 00 58  ldr	x16, 0x10000768c
	ID: 634 (ldr)
	op_count: 2
		operands[0].type: REG = x16
		operands[0].access: WRITE
		operands[1].type: MEM
		operands[1].mem.disp: 0x10000768c
		operands[1].access: READ
	Registers modified: x16

[jiegec]

Thanks! That is a copy-pasting error from master branch for capstone v5.