x86/fpu/signal: Sanitize copy_user_to_fpregs_zeroing()

Now that user_xfeatures is correctly set when xsave is enabled, remove
the duplicated initialization of components.

Rename the function while at it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121457.377341297@linutronix.de