google-ipmi-sys: Add SysPCIeSlotBifurcation subcommand placeholder

Set SysPCIeSlotBifurcation to 15 before the final implmentation is
finished to prevent it from changing as more systems depends on this
command.

Change-Id: Iea403571c65c4587c26adc09eb839768ff23a46d
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/commands.hpp b/commands.hpp
index 8471185..7eb668a 100644
--- a/commands.hpp
+++ b/commands.hpp
@@ -51,6 +51,8 @@
     SysAccelOobRead = 13,
     // Google CustomAccel service - write to a device
     SysAccelOobWrite = 14,
+    // The Sys PCIe Slot Bifurcation information command.
+    SysPCIeSlotBifurcation = 15,
 };
 
 } // namespace ipmi