gs101: use prebuilt GKI boot.img for production builds

Use:
* boot-user.img for -user builds
* boot.img for -userdebug and -eng builds

Bug: 188095549
Test: make dist (oriole-user)
Test: make dist (oriole-userdebug)
Change-Id: Ic4df227f2b4c261297272f17e6645b7ce1f5d4f3
1 file changed