make isDCMIPowerMgmtSupported cache response

isDCMIPowerMgmtSupported is called a lot if any of the DCMI commands
are used, so it makes sense to cache the value rather than constantly
re-parsing the JSON file, especially since it won't change except for
on a fw update.

Tested: DCMI power management commands continue to work as before.

Change-Id: Id0deb40c4a5332d5f96d7dda6d958f20925c01a9
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
diff --git a/dcmihandler.cpp b/dcmihandler.cpp
index ca2ee7d..8052214 100644
--- a/dcmihandler.cpp
+++ b/dcmihandler.cpp
@@ -68,9 +68,16 @@
 
 bool isDCMIPowerMgmtSupported()
 {
-    auto data = parseJSONConfig(gDCMICapabilitiesConfig);
+    static bool parsed = false;
+    static bool supported = false;
+    if (!parsed)
+    {
+        auto data = parseJSONConfig(gDCMICapabilitiesConfig);
 
-    return (gDCMIPowerMgmtSupported == data.value(gDCMIPowerMgmtCapability, 0));
+        supported = (gDCMIPowerMgmtSupported ==
+                     data.value(gDCMIPowerMgmtCapability, 0));
+    }
+    return supported;
 }
 
 uint32_t getPcap(sdbusplus::bus_t& bus)