kernel: Replace BOARD_SYSTEM_KERNEL_MODULES with SYSTEM_KERNEL_MODULES

Commit 47931c12 introduced GKI modules handling with the assumption
that using BOARD_SYSTEM_KERNEL_MODULES would still work in Android 14,
but turns out that it conflicts with build/make/core rules.

Change-Id: I9167940c08b8420be254c52698f1faa2e3e7f793