ANDROID: GKI: drivers: qcom: cmd-db: Allow compiling qcom,cmd-db driver as module

This is a hardware specific driver. So, allow compiling it as a module.

Signed-off-by: Will McVicker <willmcvicker@google.com>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Bug: 149128810
Test: compile, verify ABI is updated
Test: verify module loads on reference device
Change-Id: I98667e51914277e2009901c327db488b94dfd133