busybox/mdev.conf: Ignore eMMC RPMB and boot block devices

busybox/mdev.conf: Ignore eMMC RPMB and boot block devices

eMMC devices may report block devices like "mmcblk0rpmb" and
"mmcblk0boot0". These are not actually block devices and any
read/write operation on them will fail. To prevent spamming error
messages attempting to mount them, just ignore these devices.

(From OE-Core rev: 9f4a85eb929f67420d9689d7dddadd120ed49843)

(From OE-Core rev: 50d97edaeb18a4c6374101d222410a3b0f344bf2)

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>