package/freescale-imx: update SITE to use NXP url

package/freescale-imx: update SITE to use NXP url

NXP BSPs has been using the nxp.com URL for a while:
http://git.yoctoproject.org/cgit/cgit.cgi/meta-freescale/commit/conf/layer.conf?id=d6abbbc1ce0882bdc82e03b1868eeba1a50a7bd3

It's  unclear for how long the freescale.com redirect will be
maintained. This patch update the FREESCALE_IMX_SITE variable
to point directly to the NXP site.

Signed-off-by: Julien Olivain <juju@cotds.org>
Reviewed-by: Gary Bisson <bisson.gary@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>