x86: introduce ldt_write accessor

Create a ldt write accessor like the 32 bit one.

Preparatory patch for merging ldt.c and anyway necessary for
64bit paravirt ops.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2 files changed