drm/hisilicon/hibmc: Allow to be built if COMPILE_TEST is enabled

The commit feeb07d0 ("drm/hisilicon/hibmc: Make CONFIG_DRM_HISI_HIBMC
depend on ARM64") made the driver Kconfig symbol to depend on ARM64 since
it only supports that architecture and loading the module on others would
lead to incorrect video modes being used.

But it also prevented the driver to be built on other architectures which
is useful to have compile test coverage when doing subsystem wide changes.

Make the dependency instead to be (ARM64 || COMPILE_TEST), so the driver
is buildable when the CONFIG_COMPILE_TEST option is enabled.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20211216210936.3329977-1-javierm@redhat.com