KVM: PPC: Guard doorbell exception with CONFIG_PPC_DOORBELL
KVM: PPC: Guard doorbell exception with CONFIG_PPC_DOORBELL

Availablity of the doorbell_exception function is guarded by
CONFIG_PPC_DOORBELL. Use the same define to guard our caller
of it.

Signed-off-by: Tiejun Chen <86aa98d1ce79e67acc7976f5603381a6ff7f6a6e@windriver.com>
[agraf: improve patch description]
Signed-off-by: Alexander Graf <3ad82b0c937b9aa51276120cedd545efc822be04@suse.de>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs