i.MX: Use FREESCALE_IMX_SITE for Freescale packages

This patch consolidates the URLs for various Freescale-supplied
packages to use FREESCALE_IMX_SITE.

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
Reviewed-by: "Thomas Petazzoni" <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>