schemas: firmware: add MP5998Firmware support

Add MP5998Firmware support to I2CVRFirmware with new VR configuration
entry for Santabarbara_PDB2_VR_MP5998 and MP5998Firmware schema type.

In [1], support for updating MP5998 VR devices was introduced.

[1] https://gerrit.openbmc.org/c/openbmc/phosphor-bmc-code-mgmt/+/83050

Tested on the Santabarbara platform.

Change-Id: I31d6d24678fb3c41b9d82b7d1ea50b57a2228c2a
Signed-off-by: Freddie Jheng <Freddie.Jheng@quantatw.com>
diff --git a/schemas/firmware.json b/schemas/firmware.json
index bdf4c5c..649d04a 100644
--- a/schemas/firmware.json
+++ b/schemas/firmware.json
@@ -32,7 +32,8 @@
                         "XDPE1X2XXFirmware",
                         "ISL69269Firmware",
                         "MP2X6XXFirmware",
-                        "MP297XFirmware"
+                        "MP297XFirmware",
+                        "MP5998Firmware"
                     ]
                 },
                 "Bus": {