drm/display: Fix build error without CONFIG_OF

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: 1e0f66420b13 ("drm/display: Introduce a DRM display-helper module")
Signed-off-by: YueHaibing <[email protected]>
Reviewed-by: Dmitry Baryshkov <[email protected]>
Reviewed-by: Abhinav Kumar <[email protected]>
Acked-by: Linus Walleij <[email protected]>
Signed-off-by: Linus Walleij <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]