Move the target_disas() ARM specifics to the QOM disas_set_info hook
and delete the ARM specific code in disas.c.

This has the extra advantage of the more fully featured target_disas()
implementation now applying to monitor_disas().

Currently, target_disas() has multi-endian, thumb and AArch64
support whereas the existing monitor_disas() support only has vanilla
AA32 support.

E.G. Running an AA64 linux kernel the following -d in_asm disas happens
(taget_disas()):

IN:
0x0000000040000000:  580000c0      ldr x0, pc+24 (addr 0x40000018)
0x0000000040000004:  aa1f03e1      mov x1, xzr

However before this patch, disasing the same from the monitor:

(qemu) xp/i 0x40000000
0x0000000040000000:  580000c0      stmdapl  r0, {r6, r7}

After this patch:
(qemu) xp/i 0x40000000
0x0000000040000000:  580000c0      ldr x0, pc+24 (addr 0x40000018)
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Crosthwaite <crosthwaite.peter@gmail.com>
Signed-off-by: NAndreas Färber <afaerber@suse.de>