linux-denx: Add linux-denx repository

Add this repository since it is needed for DENX M53EVK board. The
repository contains patched kernel source fitting this board. Also
add the m53evk defconfig.

Change-Id: I544d7a1f7632332c36b2b03ec0b784da2ff6472d
Signed-off-by: Marek Vasut <marex@denx.de>
m53evk: Add DENX M53EVK support

Add DENX M53EVK board configuration file. This uses the linux-denx
kernel repository.

Change-Id: I4c7ad1446a3bf1cd5c149701861ed745025d1449
Signed-off-by: Marek Vasut <marex@denx.de>