libxl_json: introduce parser functions for builtin types

libxl_json: introduce parser functions for builtin types

This changeset introduces following functions:
 * libxl_defbool_parse_json
 * libxl__bool_parse_json
 * libxl_uuid_parse_json
 * libxl_mac_parse_json
 * libxl_bitmap_parse_json
 * libxl_cpuid_policy_list_parse_json
 * libxl_string_list_parse_json
 * libxl_key_value_list_parse_json
 * libxl_hwcap_parse_json
 * libxl__int_parse_json
 * libxl__uint{8,16,32,64}_parse_json
 * libxl__string_parse_json

They will be used in later patch to convert the libxl__json_object
tree of a builtin type to libxl_FOO struct.

Also remove declaration of libxl_domid_gen_json as libxl_domid uses
yajl_gen_integer to generate JSON object.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Anthony Perard <anthony.perard@citrix.com>