mb/dell: Add Latitude E6220 (Sandy Bridge)

mb/dell: Add Latitude E6220 (Sandy Bridge)

Mainboard is codenamed Vida. I do not physically have this system;
someone with physical access to one sent me the output of autoport which
I then modified to produce this port. The VBT was obtained using
intelvbttool while running version A14 (latest available version) of the
vendor firmware.

Tested and found to boot as part of a libreboot build based on upstream
coreboot commit b7341da191 with additional patches, though these do not
appear to affect SNB/IVB. The base E6430 patch was tested against
coreboot main.

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

Change-Id: I570023b0837521b75aac6d5652c74030c06b8a4c
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82131
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>