KVM: Export kvm_make_all_cpus_request() for use in marking VMs as bugged

Export kvm_make_all_cpus_request() and hoist the request helper
declarations of request up to the KVM_REQ_* definitions in preparation
for adding a "VM bugged" framework.  The framework will add KVM_BUG()
and KVM_BUG_ON() as alternatives to full BUG()/BUG_ON() for cases where
KVM has definitely hit a bug (in itself or in silicon) and the VM is all
but guaranteed to be hosed.  Marking a VM bugged will trigger a request
to all vCPUs to allow arch code to forcefully evict each vCPU from its
run loop.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-Id: <1d8cbbc8065d831343e70b5dcaea92268145eef1.1625186503.git.isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>