Change the naming policy of system_$(VER)

The module name of system_$(VER) prebuilt file is system_sdk_v$(VER).
But this is inconsistent with sdk_v$(LOCAL_SDK_VERSION) in
prebuilts/sdk.
So, system_sdk_v$(VER) is changed to sdk_vsystem_$(VER) to use the same
naming policy.

Bug: 72031391
Test: build
Change-Id: I3f18b7969dda208beeefdcaefadcc42db5c1577e