De-duplicate kernel module names

If BOARD_KERNEL_MODULES_16K contains duplicate kernel modules under
different directories, build will fail with 'multiple overriding
commands error' . To fix it, de-dup BOARD_KERNEL_MODULES_16K base on the
basename of kernel modules files.

Test: th
Change-Id: I45d850d5b3804c54b9ec0133d3a657c2db5adb17