drm/exynos: trigger build of all modules

Add COMPILE_TEST dependency to force exynos driver to
built for more than arm and to built modules
that otherwise required other symbols to be de-selected.

This will increase build coverage of the exynos driver
thus allowing most trivial build errors to be detected/fixed early.

This introduces one warning when built using sh:
exynos7_drm_decon.c: In function ‘decon_remove’:
exynos7_drm_decon.c:769:24: warning: unused variable ‘ctx’
  struct decon_context *ctx = dev_get_drvdata(&pdev->dev);

This is due to the definition of iounmap() in sh,
and nothing that exynos driver can fix.

Include fix of exynos build for alpha.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: Seung-Woo Kim <sw0312.kim@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Kukjin Kim <kgene@kernel.org>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Jingoo Han <jingoohan1@gmail.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>