x86/fpu: Rename copy_kernel_to_fpregs() to restore_fpregs_from_fpstate()

This is not a copy functionality. It restores the register state from the
supplied kernel buffer.

No functional changes.

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/20210623121454.716058365@linutronix.de