x86/ia32: Adds code hygiene for 32bit SYSCALL instruction entry.

x86/ia32: Adds code hygiene for 32bit SYSCALL instruction entry.

This is a followup on the 111ba91464f2e29fc6417b50a1c1425e2080bc59
(*INCOMPLETE* x86/syscall: Clear unused extra registers on syscall entrance)
where we didn't completely finish adding the clearing of these
registers. This fixes it on the  32-bit system call entrances.

The movq    R8(%rsp),%r8 is there to update the r8 as the
CLEAR_R8_TO_R15 clears that register so we have to fetch it
from the  pt_regs->r8.

We also remove the SAVE_EXTRA_REGS from the ptrace code as
we clear them (r8->r15) so the extra SAVE_EXTRA_REGS ends
up putting NULLs in the pt->regs->[r8->r15].

Orabug: 27344012
CVE:CVE-2017-5715

Reviewed-by: Kris Van Hees <kris.van.hees@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>