board/freescale/imx28evk/readme.txt: update broken url
http://freescale.com/ urls are all redirected to the NXP homepage
https://www.nxp.com/
Even if the link is not broken in the sense of a 404 http error, the
pointed resource is not found.
This commit updates the old Freescale link to the correct nxp.com
location.
Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Julien Olivain