vmm, arch, devices: Put ACPI support behind a default feature

Put the ACPI support behind a feature and ensure that the code compiles
without that feature by adding an extra build to Travis.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

arch/Cargo.toml

@@ -3,13 +3,17 @@ name = "arch"
 version = "0.1.0"
 authors = ["The Chromium OS Authors"]
 
+[features]
+default = ["acpi"]
+acpi = ["acpi_tables"]
+
 [dependencies]
 byteorder = "1.3.2"
 kvm-bindings = "0.1.1"
 kvm-ioctls = { git = "https://github.com/rust-vmm/kvm-ioctls", branch = "master" }
 libc = "0.2.60"
 
-acpi_tables = { path ="../acpi_tables" }
+acpi_tables = { path = "../acpi_tables", optional = true }
 arch_gen = { path = "../arch_gen" }
 
 [dependencies.vm-memory]

arch/src/x86_64/acpi.rs

@@ -48,7 +48,7 @@ struct PCIRangeEntry {
     pub segment: u16,
     pub start: u8,
     pub end: u8,
-    _reserved: u32
+    _reserved: u32,
 }
 
 pub fn create_dsdt_table(serial_enabled: bool) -> SDT {

arch/src/x86_64/mod.rs

@@ -183,8 +183,11 @@ pub fn configure_system(
         }
     }
 
-    let rsdp_addr = acpi::create_acpi_tables(guest_mem, num_cpus, serial_enabled);
-    params.0.acpi_rsdp_addr = rsdp_addr.0;
+    #[cfg(feature = "acpi")]
+    {
+        let rsdp_addr = acpi::create_acpi_tables(guest_mem, num_cpus, serial_enabled);
+        params.0.acpi_rsdp_addr = rsdp_addr.0;
+    }
 
     let zero_page_addr = layout::ZERO_PAGE_START;
     guest_mem