drm/i915: consider HAS_FLAT_CCS() in needs_ccs_pages

Just move the HAS_FLAT_CCS() check into needs_ccs_pages. This also then
fixes i915_ttm_memcpy_allowed() which was incorrectly reporting true on
DG1, even though it doesn't have small-BAR or flat-CCS.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/6605
Fixes: efeb3caf

 ("drm/i915/ttm: disallow CPU fallback mode for ccs pages")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220905105329.41455-1-matthew.auld@intel.com