KVM: x86/mmu: Use a bool for direct

The parameter "direct" can either be true or false, and all of the
callers pass in a bool variable or true/false literal, so just use the
type bool.

No functional change intended.

Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220516232138.1783324-3-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>