mb/dell: Add Latitude E6230 (Ivy Bridge)

mb/dell: Add Latitude E6230 (Ivy Bridge)

This was adapted from CB:22693 from Iru Cai, which was based on
autoport. I do not physically have this system. Someone with physical
access to an E6230 running version A11 of the vendor firmware sent me
the VBT after running the command `intelvbttool --inlegacy --outvbt
data.vbt`. This new version of the port has not yet been tested.

The EC is the SMSC MEC5055, which seems to be compatible with the
existing MEC5035 code. As with the other Dell systems with this EC, this
board is assumed to be internally flashable using an EC command that
tells it to pull the FDO pin low on the next boot, which also tells the
vendor firmware to disable all write protections to the flash [1].

[1] https://gitlab.com/nic3-14159/dell-flash-unlock

Original-Change-Id: I8cdc01e902e670310628809416290045c2102340
Change-Id: I32927beea7c29b96a851ab77ed15b0160f16d369
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82153
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>