x86/capabilities: set/clear them using non-locked bitops

x86/capabilities: set/clear them using non-locked bitops

Their initialization happens without races, so there's no point in
using atomic (locked) operations to update the respective flags.
(There's one case where the clear_bit() was completely pointless.)

Also drop a neighboring stale comment from AMD code.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>