ARM: at91: uncompress: autodetect the uart to use

This will now autodetect the first uart enabled by the bootloader
and will use it for uncompress. This will still assume that the bootloader
configured it (pins and clock).

This also allows to include all soc headers together.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>