Passed kUsb and kSd flags

Initially, we were thinking to pass kInternal for non usb drive/sd card
drive (for local external storage like directory shared from ChromeOS).
Fortunately, the DocumentsUI logic apparently has TYPE_LOCAL with
R.drawable.ic_root_smartphone (that is overlayable) for external storage
other than TYPE_USB and TYPE_SD.

Therefore, instead of creating a kInternal flags, we can just passed kUsb
and kSd and not passing anything for "internal external storage" - which
will render ic_root_usb, ic_root_sd, and ic_root_smartphone as icons
accordingly. And since ic_root_smartphone is already overlayable,  we
could overlayed in /vendor - which effectively is what we initially
wanted when thinking of introducing kInternal flag.

Bug: 132796154
Test: Customize flags in /vendor for different devices and DocumentsUI
shows the ic_root_smartphone (which can be overlayed) when kUsb is not
passed, and USB icon when kUsb is passed.
Change-Id: I55f13e214bbb2aeed96b6950bcf391121174c354