This patch is to 'Add ARM64 support to peekfd'.

This patch is to 'Add ARM64 support to peekfd'.

ARM64 copy user_pt_regs to user space instead of pt_regs.
So in this patch, mapping the require user_pt_regs except orig_x0,
as orig_x0 not available in user_pt_regs for SYSCALL exit.

For each SYSCALL, peekfd catches user_pt_regs for SYSCALL entry/exit.
Value of orig_x0 is available in user_pt_regs->x0 of SYSCALL entry.

So to get orig_x0, stores user_pt_regs of SYSCALL entry,
and then compare 'fd and addr of buffer' of  SYSCALL exit
with SYSCALL entry to retrive orig_x0 at the time of SYSCALL exit.

Signed-off-by: Ajay Kaher <akaher@vmware.com>