x86/fpu: Rename 'xsave_hdr' to 'header'

Code like:

           fpu->state->xsave.xsave_hdr.xstate_bv |= XSTATE_FP;

is an eyesore, because not only is the words 'xsave' and 'state'
are repeated twice times (!), but also because of the 'hdr' and 'bv'
abbreviations that are pretty meaningless at a first glance.

Start cleaning this up by renaming 'xsave_hdr' to 'header'.

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/include/uapi/asm/sigcontext.h

@@ -209,7 +209,7 @@ struct sigcontext {
 
 #endif /* !__i386__ */
 
-struct _xsave_hdr {
+struct _header {
 	__u64 xstate_bv;
 	__u64 reserved1[2];
 	__u64 reserved2[5];
@@ -228,7 +228,7 @@ struct _ymmh_state {
  */
 struct _xstate {
 	struct _fpstate fpstate;
-	struct _xsave_hdr xstate_hdr;
+	struct _header xstate_hdr;
 	struct _ymmh_state ymmh;
 	/* new processor state extensions go here */
 };