armhf: config: Disable XEN

Enable Xen forces CONFIG_ARCH_DMA_ADDR_T_64BIT=y even on 32 bit arm;
Which unfortunately exposes bugs in the CAAM driver. Disable it for now
as we don't care about it for Apertis.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>