audiopolicy: Refactor HwModuleCollection

 -- make AudioPolicyManager::mHwModules to only store
    loaded modules; all modules stored in mHwModulesAll;
    this removes lots of checks for HwModule::mHandle;

 -- use "for range" loops when iterating over mHwModules;

 -- use HwModulesCollection::getModuleFromName for finding
    the remote submix module;

 -- log statements print HwModule's name instead of index.

Test: audio still works
Change-Id: I2d86caae23e87e25b6a367cb4042741f0b32e99c