PEL: move jsonCalloutSubtype const definition to header

SBE FFDC need to consume this constant to create json
callout type file creation.

Signed-off-by: Jayanth Othayoth <ojayanth@in.ibm.com>
Change-Id: I71eeccbb478d7cec5bfc8b1844c11f641d8a388b
diff --git a/extensions/openpower-pels/pel.hpp b/extensions/openpower-pels/pel.hpp
index 8b592f7..884379a 100644
--- a/extensions/openpower-pels/pel.hpp
+++ b/extensions/openpower-pels/pel.hpp
@@ -30,6 +30,8 @@
 
 using PelFFDC = std::vector<PelFFDCfile>;
 
+constexpr uint8_t jsonCalloutSubtype = 0xCA;
+
 /** @class PEL
  *
  * @brief This class represents a specific event log format referred to as a