x86: add support for Meraki MX100

x86: add support for Meraki MX100

This commit will add support for the Meraki MX100 in OpenWRT.

Specs:
* CPU: Intel Xeon E3-1200 Series 1.5GHz 2C/4T
* Memory: 4GB DDR3 1600 ECC
* Storage: 1GB USB NAND, 1TB SATA HDD
* Wireless: None
* Wired: 10x 1Gb RJ45, 2x 1Gb SFP

UART:
The UART header is named CONN11 and is found in the
center of the mainboard. The pinout from Pin 1 (marked
with a black triangle) to pin 4 is below:
Pin 1: VCC
Pin 2: TX
Pin 3: RX
Pin 4: GND
Note that VCC is not required for UART on this device.

Booting:
1. Flash/burn one of the images from this repo to a
flash drive.
2. Take the top off the MX100, and unplug the SATA
cable from the HDD.
3. Hook up UART to the MX100, plug in the USB drive,
and then power up the device.
4. At the BIOS prompt, quickly press F7 and then
scroll to the Save & Exit tab.
5. Scroll down to Boot Override, and select the
UEFI entry for your jumpdrive.

Note: UEFI booting will fail if the SATA cable for
the HDD is plugged in.
The issue is explained under the Flashing instructions.

Flashing:
1. Ensure the MX100 is powered down, and not plugged
into power.
2. Take the top off the MX100, and unplug the SATA
cable from the HDD.
3. Using the Mini USB female port found by the SATA
port on the motherboard,
flash one of the images to the system. Example:
`dd if=image of=/dev/sdb conv=fdatasync` where sdb
is the USB device for the MX100's NAND.
4. Unplug the Mini USB, hook up UART to the MX100,
and then power up the device.
5. At the BIOS prompt, quickly press F7 and then
scroll to the Boot tab.
6. Change the boot order and set UEFI: USB DISK 2.0
as first, and USB DISK 2.0 as second.
Disable the other boot options.
7. Go to Save & Exit, and then select Save Changes and
Reset

Note that OpenWRT will fail to boot in UEFI mode when
the SATA hard drive is plugged in. To fix this, boot
with the SATA disk unplugged and then run the following
command:
`sed -i "s|hd0,gpt1|hd1,gpt1|g" boot/grub/grub.cfg`
Once the above is ran, OpenWRT will boot when the HDD
is plugged into SATA. The reason this happens is the
UEFI implementation for the MX100 will always set
anything on SATA to HD0 instead of the onboard USB
storage, so we have to accomidate it since OpenWRT's
GRUB does not support detecting a boot disk via UUID.

Signed-off-by: Chris Blake <chrisrblake93@gmail.com>