include: add SPDX GPL-2.0-only license tags for files without licensing information ...

According to our /README, GPL-2.0-only applies for the whole project
except noted otherwise.

Signed-off-by: Roland Hieber <rohieb@rohieb.name>
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

add basic at91sam9260 support. Currently only second stage ...

bootloader is supported:
- No SDRAM initialisation
- No UART init / baudrate change