KVM: Merge kvm_ioapic_get_delivery_bitmask into kvm_get_intr_delivery_bitmask

Gleb fixed bitmap ops usage in kvm_ioapic_get_delivery_bitmask.

Sheng merged two functions, as well as fixed several issues in
kvm_get_intr_delivery_bitmask
1. deliver_bitmask is a bitmap rather than a unsigned long intereger.
2. Lowest priority target bitmap wrong calculated by mistake.
3. Prevent potential NULL reference.
4. Declaration in include/kvm_host.h caused powerpc compilation warning.
5. Add warning for guest broadcast interrupt with lowest priority delivery mode.
6. Removed duplicate bitmap clean up in caller of kvm_get_intr_delivery_bitmask.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>