drm/tiny: add missing MODULE_DESCRIPTION() macros

make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tiny/bochs.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tiny/cirrus.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/gpu/drm/tiny/gm12u320.o

Add the missing invocations of the MODULE_DESCRIPTION() macro.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240609-md-drivers-gpu-drm-tiny-v1-1-6905fe4ada50@quicinc.com