add support for rainier 1s4u

The rainier 1s4u is very similar to the standard rainier 4u. It will
have a different device tree but the only change from the 4u is two
less fans.

Tested:
- Updated IM keyword to that of 1s4u and re-ran system-vpd service.
  Verified that u-boot fitconfig env variable was correctly set to
  conf@aspeed-bmc-ibm-rainier-1s4u.dtb

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I3507e0239283dc700bd0834b66a46ff0c6deeba7
diff --git a/const.hpp b/const.hpp
index 9eafc4b..5c67968 100644
--- a/const.hpp
+++ b/const.hpp
@@ -49,6 +49,7 @@
 static constexpr auto INVALID_NODE_NUMBER = -1;
 static constexpr auto RAINIER_2U = "50001001";
 static constexpr auto RAINIER_4U = "50001000";
+static constexpr auto RAINIER_1S4U = "50001002";
 static constexpr auto EVEREST = "50003000";
 
 constexpr uint8_t KW_VPD_START_TAG = 0x82;