layers: Add VkFlags parameter validation

Add parameter validation for VkFlags derived types to the
parameter_validation layer's code generation scripts.  The following
validation checks are performed:
 - If a VkFlags parameter is not marked as optional in the XML, a message
   is generated when the parameter is 0.
 - If a VkFlags parameter is not 0, a message is generated if it combines
   bits that are not defined by its associated flag bits enumeration.
 - If a VkFlags parameter does not have an associated flag bits
   enumeration it is treated as a reserved value that must be 0.

Change-Id: I6daed360cde46e2a27c84deda1e0798621f92d50
2 files changed