arm64: xilinx: Guard distro boot variable generation

When distro boot is disabled there is no reason to generate variables for
it. Also do not update boot_targets variable because it would be unused.

It is useful for example when standard boot is enabled and distro boot
is disabled.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/570c51435da59831ec245cddceda078afa58a550.1693913398.git.michal.simek@amd.com
6 files changed