Fix USB enumeration on OS X (#640)

Hopefully without breaking the others.

Summary of the changes:
- Device descriptor reports the device is bus powered and requires
  100mA max.
- HID descriptor version bumped to 1.11 (was 1.10)
- Added string index for Interface and HID descriptors (which seems to
  make OS X happy)

patches/tock/04-vendor-hid.patch

@@ -10,7 +10,7 @@ index 65301bcf1..dc70e98b1 100644
 +[features]
 +vendor_hid = []
 diff --git a/capsules/src/usb/descriptors.rs b/capsules/src/usb/descriptors.rs
-index 67f708239..c2556d3a2 100644
+index 9c5bc9cd1..c3ed71c44 100644
 --- a/capsules/src/usb/descriptors.rs
 +++ b/capsules/src/usb/descriptors.rs
 @@ -415,13 +415,14 @@ impl DescriptorBuffer {