rootdev: Use large file support (LFS)

Without LFS, stat fails with -EOVERFLOW on devices with major:minor
numbers that don't fit within 8 bits on 32-bit architecutres. This
patch turns on LFS to allow that, fixing a bringup but on a new
platform.

BUG=chromium:464024
TEST=Booted onto a machine and successfully ran rootdev with a large
major:minor number.

Change-Id: I3dfe698e65366f4608705f56894988d2643e375f
Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/258550


Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>