drivers: power: reset: Fix build errors in msm-reset module

* If the QCOM hardreboot implementation is disabled, *_dload_mode
  functions will never be used and this will raise an unused function
  warning during the build.

So we can disable *_dload_mode when QCOM hardreboot is not enabled.

Change-Id: I360b057ee9aca0513d45c64274198ac8dd7eea73