x86/fpu: Merge the two code paths in __fpu__restore_sig()

The ia32_fxstate case (32bit with fxsr) and the other (64bit frames or
32bit frames without fxsr) restore both from kernel memory and sanitize
the content.

The !ia32_fxstate version restores missing xstates from "init state"
while the ia32_fxstate doesn't and skips it.

Merge the two code paths and keep the !ia32_fxstate one. Copy only the
user_i387_ia32_struct data structure in the ia32_fxstate.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190403164156.19645-23-bigeasy@linutronix.de