x86/ptrace: Always inline v8086_mode() for instrumentation

Instrumentation glue like KASAN causes the following warning:

  vmlinux.o: warning: objtool: mce_gather_info()+0x5f: call to v8086_mode.constprop.0() leaves .noinstr.text section

due to gcc creating a function call for that oneliner. Force-inline it
and even save some vmlinux bytes (.config is close to an allmodconfig):

     text    data     bss     dec     hex filename
  209431677       208257651       34411048        452100376       1af28118	vmlinux.before
  209431519       208257615       34411048        452100182       1af28056	vmlinux.after
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Marco Elver <elver@google.com>
Link: https://lore.kernel.org/r/20220204083015.17317-3-bp@alien8.de

arch/x86/include/asm/ptrace.h

@@ -137,7 +137,7 @@ static __always_inline int user_mode(struct pt_regs *regs)
 #endif
 }
 
-static inline int v8086_mode(struct pt_regs *regs)
+static __always_inline int v8086_mode(struct pt_regs *regs)
 {
 #ifdef CONFIG_X86_32
 	return (regs->flags & X86_VM_MASK);