x86/sev-es: Leave NMI-mode before sending signals

The error path in the runtime #VC handler sends a signal to kill the
current task if the exception was raised from user-space. Some parts of
the #VC handler run in NMI mode, because it is critical that it is not
interrupted (except from an NMI) while the GHCB is in use.

But sending signals in NMI-mode is actually broken and triggers lockdep
warnings. On the other side, when the signal is sent, there is no reason
for the handler to still be in NMI-mode, as the GHCB is not used
anymore.

Leave NMI-mode before entering the error path to get rid of the lockdep
warnings.

Fixes: 62441a1fb532 ("x86/sev-es: Correctly track IRQ states in runtime #VC handler")
Signed-off-by: Joerg Roedel <jroedel@suse.de>