Documentation: boards: stm32mp: document boot error LED ...

The STM32MP Evaluation Kits place a LED on PA13 to display boot status.
Document its blinking patterns.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: boards: stm32mp: document boot mode strap pins ...

The evaluation kits have 2P DIP-Switches for boot mode selection.
Document them.

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: boards: stm32mp: remove done TODOs ...

With SD/MMC controller and Ethernet MAC support merged, we now have
usable STM32MP support. Remove the text that suggested otherwise.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: boards: stm32mp: document environment partition ...

We have barebox get its environment out of a "barebox-environment"
partition. The BootROM and first stage bootloader both select partitions
on name not UUID, so we're following suit.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: boards: add initial STM32MP documentation ...

Support for the SoC is still in progress, but lets document
what we have now.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>