x86/fpu: Remove xsave_init() __init obfuscation

So this code surprised me - and being surprised when reading FPU code
does not help maintainability of an already overly complex subsystem.

Remove the obfuscation and just don't use __init annotation for now.
Anyone who wants to free these ~600 bytes of xstate_enable_boot_cpu()
should implement it cleanly.
Reviewed-by: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/fpu/xsave.c

@@ -606,8 +606,11 @@ static void __init init_xstate_size(void)
 
 /*
  * Enable and initialize the xsave feature.
+ *
+ * ( Not marked __init because of false positive section warnings
+ *   generated by xsave_init(). )
  */
-static void __init xstate_enable_boot_cpu(void)
+static void /* __init */ xstate_enable_boot_cpu(void)
 {
 	unsigned int eax, ebx, ecx, edx;
 
@@ -663,21 +666,20 @@ static void __init xstate_enable_boot_cpu(void)
 /*
  * For the very first instance, this calls xstate_enable_boot_cpu();
  * for all subsequent instances, this calls xstate_enable().
- *
- * This is somewhat obfuscated due to the lack of powerful enough
- * overrides for the section checks.
  */
 void xsave_init(void)
 {
-	static __refdata void (*next_func)(void) = xstate_enable_boot_cpu;
-	void (*this_func)(void);
+	static char on_boot_cpu = 1;
 
 	if (!cpu_has_xsave)
 		return;
 
-	this_func = next_func;
-	next_func = xstate_enable;
-	this_func();
+	if (on_boot_cpu) {
+		on_boot_cpu = 0;
+		xstate_enable_boot_cpu();
+	} else {
+		xstate_enable();
+	}
 }
 
 /*