x86/entry/64: Drop idtentry's manual stack switch for user entries

For non-paranoid entries, idtentry knows how to switch from the
kernel stack to the user stack, as does error_entry.  This results
in pointless duplication and code bloat.  Make idtentry stop
thinking about stacks for non-paranoid entries.

This reduces text size by 5377 bytes.

This goes back to the following commit:

  7f2590a1 ("x86/entry/64: Use a per-CPU trampoline stack for IDT entries")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/90aab80c1f906e70742eaa4512e3c9b5e62d59d4.1522794757.git.luto@kernel.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/entry/entry_64.S

@@ -908,7 +908,7 @@ ENTRY(\sym)
 	pushq	$-1				/* ORIG_RAX: no syscall to restart */
 	.endif
 
-	.if \paranoid < 2
+	.if \paranoid == 1
 	testb	$3, CS-ORIG_RAX(%rsp)		/* If coming from userspace, switch stacks */
 	jnz	.Lfrom_usermode_switch_stack_\@
 	.endif
@@ -955,7 +955,7 @@ ENTRY(\sym)
 	jmp	error_exit
 	.endif
 
-	.if \paranoid < 2
+	.if \paranoid == 1
 	/*
 	 * Entry from userspace.  Switch stacks and treat it
 	 * as a normal entry.  This means that paranoid handlers