x86: x86 ptrace getreg/putreg cleanup

This cleans up the getreg/putreg functions to move the special cases
(segment registers and eflags) out into their own subroutines.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>