android_mtdutils: Add mtd_node_info

Add a function mtd_node_info to read MTD device info from a
device node name. Also refactor mtd_partition_info to use
this function.

BUG=chromium:426742
TEST=emerge android_mtdutils

Change-Id: I129bcb3e06cb3664f4f94de81cb34bcc405e7b51
Reviewed-on: https://chromium-review.googlesource.com/234454
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Gaurav Shah <gauravsh@chromium.org>
Commit-Queue: Gaurav Shah <gauravsh@chromium.org>
2 files changed