Update FRU part number for PowerVS systems

Error log makes use of FRU part number instead of part number in the
call outs.
Hence the code is updated to change FRU part number instead of part
number in case of PowerVS systems.
Similarly, spare part number of Decorator.Asset interface is updated
instead of part number.

Change-Id: I31b57e23863b250f7fb036b23c7a192fc1bbec5c
Signed-off-by: Sunny Srivastava <sunnsr25@in.ibm.com>
diff --git a/vpd-manager/include/constants.hpp b/vpd-manager/include/constants.hpp
index f71b18e..e605cd1 100644
--- a/vpd-manager/include/constants.hpp
+++ b/vpd-manager/include/constants.hpp
@@ -139,6 +139,7 @@
 constexpr auto kwdHW = "HW";
 constexpr auto kwdIM = "IM";
 constexpr auto kwdPN = "PN";
+constexpr auto kwdFN = "FN";
 constexpr auto recVSYS = "VSYS";
 constexpr auto recVCEN = "VCEN";
 constexpr auto locationCodeInf = "com.ibm.ipzvpd.Location";