hvf: arm: Ignore cache operations on MMIO

Apple's Hypervisor.Framework forwards cache operations as MMIO traps
into user space. For MMIO however, these have no meaning: There is no
cache attached to them.

So let's just treat cache data exits as nops.

This fixes OpenBSD booting as guest.

Reported-by: AJ Barris <AwlsomeAlex@github.com>
Signed-off-by: Alexander Graf <agraf@csgraf.de>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Reference: https://github.com/utmapp/UTM/issues/3197


Message-Id: <20211026071241.74889-1-agraf@csgraf.de>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>