arm64: print instructions leading to exception

arm64: print instructions leading to exception

If an exception occurs in a loaded image and the relocation offset is
unknown, it is helpful to know the instructions pointed to by the
program counter. This patch adds the missing output.

A possible output is:
    Code: 910c4021 aa1303e0 f9400662 d63f0040 (e7f7defb)

The parentheses indicate the instruction causing the exception.

The output can be disassembled using scripts/decodecode:

echo 'Code: 90000360 9100b800 94002782 17ffff8f (e7f7defb)' | \
  ARCH=arm64 scripts/decodecode

Code: 90000360 9100b800 94002782 17ffff8f (e7f7defb)
All code
========
   0:   90000360    adrp    x0, 0x6c000
   4:   9100b800    add     x0, x0, #0x2e
   8:   94002782    bl      0x9e10
   c:   17ffff8f    b       0xfffffffffffffe48
  10:*  e7f7defb    .inst   0xe7f7defb ; undefined <-- trapping instruction

Code starting with the faulting instruction
===========================================
   0:   e7f7defb    .inst   0xe7f7defb ; undefined

We already have implemented the same for armv7.

For testing command 'exception undefined' can be used.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>