percpu: remove per_cpu__ prefix.

Now that the return from alloc_percpu is compatible with the address
of per-cpu vars, it makes sense to hand around the address of per-cpu
variables.  To make this sane, we remove the per_cpu__ prefix we used
created to stop people accidentally using these vars directly.

Now we have sparse, we can use that (next patch).

tj: * Updated to convert stuff which were missed by or added after the
      original patch.

    * Kill per_cpu_var() macro.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>

arch/x86/kernel/head_32.S

@@ -438,8 +438,8 @@ is386:	movl $2,%ecx		# set MP
 	 */
 	cmpb $0,ready
 	jne 1f
-	movl $per_cpu__gdt_page,%eax
-	movl $per_cpu__stack_canary,%ecx
+	movl $gdt_page,%eax
+	movl $stack_canary,%ecx
 	movw %cx, 8 * GDT_ENTRY_STACK_CANARY + 2(%eax)
 	shrl $16, %ecx
 	movb %cl, 8 * GDT_ENTRY_STACK_CANARY + 4(%eax)
@@ -702,7 +702,7 @@ idt_descr:
 	.word 0				# 32 bit align gdt_desc.address
 ENTRY(early_gdt_descr)
 	.word GDT_ENTRIES*8-1
-	.long per_cpu__gdt_page		/* Overwritten for secondary CPUs */
+	.long gdt_page			/* Overwritten for secondary CPUs */
 
 /*
  * The boot_gdt must mirror the equivalent in setup.S and is