boot: pxe_utils: Do not use fdtcontroladdr for FIT Image format

When patch [1] introduced "fdtcontroladdr" fallback in order to use
built-in DT when no DT in provided in PXE config, it broke FIT image
boot where the DT from the FIT configuration was used.

This disables the "fdtcontroladdr" fallback when the provided
image is from the FIT image type.

[1] d5ba6188 ("cmd: pxe_utils: Check fdtcontroladdr in label_boot")

Fixes: d5ba6188 ("cmd: pxe_utils: Check fdtcontroladdr in label_boot")
Cc: Tom Rini <trini@konsulko.com>
Cc: Peter Hoyes <peter.hoyes@arm.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>