x86/fpu/signal: Use fpstate for size and features

For dynamically enabled features it's required to get the features which
are enabled for that context when restoring from sigframe.

The same applies for all signal frame size calculations.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/87ilxz5iew.ffs@tglx