KVM: arm64: Commit exceptions from KVM_SET_VCPU_EVENTS immediately

syzkaller has found that it can trip a warning in KVM's exception
emulation infrastructure by repeatedly injecting exceptions into the
guest.

While it's unlikely that a reasonable VMM will do this, further
investigation of the issue reveals that KVM can potentially discard the
"pending" SEA state. While the handling of KVM_GET_VCPU_EVENTS presumes
that userspace-injected SEAs are realized immediately, in reality the
emulated exception entry is deferred until the next call to KVM_RUN.

Hack-a-fix the immediate issues by committing the pending exceptions to
the vCPU's architectural state immediately in KVM_SET_VCPU_EVENTS. This
is no different to the way KVM-injected exceptions are handled in
KVM_RUN where we potentially call __kvm_adjust_pc() before returning to
userspace.

Reported-by:  <syzbot+4e09b1432de3774b86ae@syzkaller.appspotmail.com>
Reported-by:  <syzbot+1f6f096afda6f4f8f565@syzkaller.appspotmail.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>