meta-palmetto: Use mboxd instead of aspeed-lpc-ctrl

Palmetto is going to enable phosphor-isolation, which requires to use
mbox for PNOR access instead of directly mapping on LPC to PNOR.

Tested: With Palmetto's [dts fix][1] and a PNOR build that enables
        [PNORDD_IS_IPMI][2], verify Palmetto boots host successfully.

[1]: https://patchwork.ozlabs.org/patch/1042662
[2]: https://github.com/open-power/op-build/pull/2680

Change-Id: I60e26903c81fc0f14b12c4ffe6915311b087b7b2
Signed-off-by: Lei YU <mine260309@gmail.com>
1 file changed