drm/arm: Kconfig annotate drivers as COMPILE_TEST

Add the COMPILE_TEST conditional, so that people can at least build test
the drivers.

Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Brian Starkey <brian.starkey@arm.com>
Cc: Mali DP Maintainers <malidp@foss.arm.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Tested-by: Liviu Dudau <liviu.dudau@arm.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200517193655.3895087-1-emil.l.velikov@gmail.com