Building firmware supported by coreboot

Intro

Tested on Ubuntu 16.04 LTS
CPU with 4 threads is used in instruction as an example
Example PLATFORM_IP of PC Engines platform is 192.168.0.102
Git is required (type sudo apt-get install git -y to install git)

Coreboot ROM building process

Build environment container.
Clone coreboot repository:
```
git clone https://review.coreboot.org/coreboot.git
```
And download submodules:
```
cd coreboot
git submodule update --init --checkout
```
Changing files in downloaded directory is not required and it may cause that built coreboot ROM will be labeled as dirty. This is an undesirable situation.

Run docker container:

docker run --rm     -v ${PWD}:/workdir     -t -i pc-engines/apu2 bash

Build crossgcc: > It's required only on first run.
```
cd /workdir/coreboot
make crossgcc-i386 CPUS=4
```
In place of 4 in CPUS=4 type number of threads you want to use.

Configure your build: If previously you've built a ROM for another platform you should clean configuration. You make it so by typing:

make distclean

Configure your build parameters:

make menuconfig

Menu with build options should be shown.

Select correct options: * For ALIX.1 series:

Mainboard ---> Mainboard vendor ---> PC Engines
Mainboard ---> Mainboard model  ---> ALIX.1C
Mainboard ---> ROM chip size    ---> 1024 KB (1 MB)

* For ALIX.2, ALIX.3 series:

Mainboard ---> Mainboard vendor ---> PC Engines
Mainboard ---> Mainboard model  ---> ALIX.2D2 or 2D3
Mainboard ---> ROM chip size    ---> 1024 KB (1 MB)

* For ALIX.6 series

Mainboard ---> Mainboard vendor ---> PC Engines
Mainboard ---> Mainboard model  ---> ALIX.6
Mainboard ---> ROM chip size    ---> 1024 KB (1 MB)

* For APU1 series:

Mainboard ---> Mainboard vendor ---> PC Engines
Mainboard ---> Mainboard model  ---> APU1

* For APU2 series

Mainboard ---> Mainboard vendor ---> PC Engines
Mainboard ---> Mainboard model  ---> APU2

To enable creating coreboot boot timestamps table select:

General setup ---> [ ]Create a table of timestamps collected during boot

Then press Y key to enable that function. If enabled, * should appear:

[*]Create a table of timestamps collected during boot

Build coreboot ROM file:
```
make CPUS=4
```
> In place of 4 in CPUS=4 type number of threads you want to use.

Built ROM should be in build directory and it may be named coreboot.rom.
You can now send it to the target device. E.g. with scp usage:
```
scp build/coreboot.rom root@192.168.0.102:/tmp
```