Add VcnLocation to reflect the VCN build system flag value

This patch defines VcnLocation.IS_VCN_IN_MAINLINE to reflect the
value of the build system flag RELEASE_MOVE_VCN_TO_MAINLINE.

Specifically two versions of VcnLocation file are defined. The build
system flag controls which VcnLocation file will be built in to the
platform. As results, the platform can read the value of
IS_VCN_IN_MAINLINE to know the value of the build system flag.

Bug: 375213246
Test: build-flag set RELEASE_MOVE_VCN_TO_MAINLINE and
      verified IS_VCN_IN_MAINLINE value
Flag: RELEASE_MOVE_VCN_TO_MAINLINE
Change-Id: I550fe1cc8a582b672281fd816804726a56531ca4