chromeos-config: add psu type cros-config fallback command

This command allows pre-unibuild devices to set the psu-type key for the
hardware-properties field. cros-healthd uses this field to determine if
the device has a battery.

BUG=chromium:1114358
TEST=emerge-bob chromeos-config-tools
cros deploy dut chromeos-config-tools
(dut) cat /run/chromeos-config/v1/hardware-properties/psu-type (battery)

Change-Id: I10aa0bad3b10242f7e62f328487999fdb3cd7ad4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2347124
Commit-Queue: Trent Begin <tbegin@chromium.org>
Tested-by: Trent Begin <tbegin@chromium.org>
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
diff --git a/chromeos-config/libcros_config/cros_config_fallback.cc b/chromeos-config/libcros_config/cros_config_fallback.cc
index a91bda4..3bd9826 100644
--- a/chromeos-config/libcros_config/cros_config_fallback.cc
+++ b/chromeos-config/libcros_config/cros_config_fallback.cc
@@ -35,7 +35,8 @@
   {"/", "name", "mosys platform model"},
   {"/", "brand-code", "mosys platform brand"},
   {"/identity", "sku-id", "mosys platform sku"},
-  {"/identity", "platform-name", "mosys platform name"}};
+  {"/identity", "platform-name", "mosys platform name"},
+  {"/hardware-properties", "psu-type", "mosys psu type"}};
 
 }  // namespace