drm/display: Fix build error without CONFIG_OF

While CONFIG_OF is n but COMPILE_TEST is y, we got this:

WARNING: unmet direct dependencies detected for DRM_DP_AUX_BUS
  Depends on [n]: HAS_IOMEM [=y] && DRM [=y] && OF [=n]
  Selected by [y]:
  - DRM_MSM [=y] && HAS_IOMEM [=y] && DRM [=y] && (ARCH_QCOM || SOC_IMX5 || COMPILE_TEST [=y]) && COMMON_CLK [=y] && IOMMU_SUPPORT [=y] && (QCOM_OCMEM [=n] || QCOM_OCMEM [=n]=n) && (QCOM_LLCC [=y] || QCOM_LLCC [=y]=n) && (QCOM_COMMAND_DB [=n] || QCOM_COMMAND_DB [=n]=n)

Make DRM_DP_AUX_BUS depends on OF || COMPILE_TEST to fix this warning.

Fixes: 1e0f6642 ("drm/display: Introduce a DRM display-helper module")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220611041612.1976-1-yuehaibing@huawei.com

drivers/gpu/drm/display/Kconfig

@@ -3,7 +3,7 @@
 config DRM_DP_AUX_BUS
 	tristate
 	depends on DRM
-	depends on OF
+	depends on OF || COMPILE_TEST
 
 config DRM_DISPLAY_HELPER
 	tristate