psu-ng: Update supported configuration properties

The Supported Configuration schema has been updated to have a single
model instead of array of models, and to have an array of input voltages
instead of a single voltage.
In addition, update the name of the supported number of power supplies
from max to count, so that it better reflects that a specific number of
power supplies are expected, and not an 'up to' max number.

Change-Id: I7a4bfa9b195ce7b9d13802dbb234018c6f217fda
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/utility.hpp b/utility.hpp
index 51fe31d..941c909 100644
--- a/utility.hpp
+++ b/utility.hpp
@@ -29,8 +29,7 @@
 using DbusInterfaceList = std::vector<DbusInterface>;
 using DbusSubtree =
     std::map<DbusPath, std::map<DbusService, DbusInterfaceList>>;
-using DbusVariant =
-    std::variant<uint64_t, std::string, std::vector<std::string>>;
+using DbusVariant = std::variant<uint64_t, std::string, std::vector<uint64_t>>;
 using DbusPropertyMap = std::map<DbusProperty, DbusVariant>;
 /**
  * @brief Get the service name from the mapper for the