tended as a
preliminary step in unifying this code between architectures.

Also, be a bit more strict in truncating 32-bit "extended" segment
register values to 16 bits.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>