init: modify mount process on diag

init: modify mount process on diag

When the system-as-root feature is enabled, kernel
uses ramdisk in system partition, it causes Diag
ramdisk (factory_ramdisk) doesn't be mounted.
The change modify kernel mount process to use original
ramdisk when compiling the Diag kerenl.

Bug 200449814

Change-Id: Ibdeead4df720a539b517c3fa95a384c244a514bb
Signed-off-by: Frank Chueh <fchueh@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1930595
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Ian Chang <ianc@nvidia.com>
Reviewed-by: Vinayak Pane <vpane@nvidia.com>
Reviewed-by: Daniel Fu <danifu@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>