x86/fpu: Provide a proper function for ex_handler_fprestore()

x86/fpu: Provide a proper function for ex_handler_fprestore()

BugLink: https://bugs.launchpad.net/bugs/1967750
To make upcoming changes for support of dynamically enabled features
simpler, provide a proper function for the exception handler which removes
exposure of FPU internals.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211015011540.053515012@linutronix.de
(cherry picked from commit 079ec41b22b952cdf3126527d735e373c9125f6d)
Acked-by: Dimitri John Ledkov <dimitri.ledkov@canonical.com>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>