x86/percpu: Use static initializer for GDT entry

The IDT cleanup is about to remove pack_descriptor(). The GDT setup for the
per-cpu storage can be achieved with the static initializer as well. Replace
it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170828064957.954214927@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/setup_percpu.c

@@ -155,13 +155,10 @@ static void __init pcpup_populate_pte(unsigned long addr)
 static inline void setup_percpu_segment(int cpu)
 {
 #ifdef CONFIG_X86_32
-	struct desc_struct gdt;
+	struct desc_struct d = GDT_ENTRY_INIT(0x8092, per_cpu_offset(cpu),
+					      0xFFFFF);
 
-	pack_descriptor(&gdt, per_cpu_offset(cpu), 0xFFFFF,
-			0x2 | DESCTYPE_S, 0x8);
-	gdt.s = 1;
-	write_gdt_entry(get_cpu_gdt_rw(cpu),
-			GDT_ENTRY_PERCPU, &gdt, DESCTYPE_S);
+	write_gdt_entry(get_cpu_gdt_rw(cpu), GDT_ENTRY_PERCPU, &d, DESCTYPE_S);
 #endif
 }