aspeed: move MTD partition rules

Move the MTD partition rules to their own recipe under
udev rather than appending u-boot-fw-utils.  Additionally
the rules are an artifact of the aspeed u-boot-fw-utils
configuration, so place the new recipe in the aspeed layer.

Tested: Built a witherspoon image
Change-Id: I1fec995dd75543b2630db29d78bfb29a1a5949d5
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
3 files changed