hw/microblaze: Remove the big-endian variants of ml605 and xlnx-zynqmp-pmu

hw/microblaze: Remove the big-endian variants of ml605 and xlnx-zynqmp-pmu

Both machines were added with little-endian in mind only (the
"endianness" CPU property was hard-wired to "true", see commits
133d23b3ad1 and a88bbb006a52), so the variants that showed up
on the big endian target likely never worked. We deprecated these
non-working machine variants two releases ago, and so far nobody
complained, so it should be fine now to disable them. Hard-wire
the machines to little endian now.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20250515132019.569365-4-thuth@redhat.com>