Also create dirs under /first_stage_ramdisk for GKI.

If the device uses GKI and generic ramdisk, also create
empty directories under /first_stage_ramdisk so that they
won't have to be created at runtime. This allows generic
ramdisk to be not writable.

Test: boots
Bug: 173425293
Change-Id: If987cb1d4af9f9ee94a43a4523f9e1465b01b16a