linux-denx: Restrict recipe compatibility for m53evk

This fixes following warning, when building other mx5 boards:

,----
| WARNING: Unable to get checksum for linux-denx SRC_URI entry
|     defconfig: file could not be found
`----

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
u-boot-cubox-i: update to a06fada55a SRCREV

This patch updates the revision to a06fada55a.
Updates include added support for ramdisks.

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>