drm/i915/icl: Don't update enabled dbuf slices struct until updated in hw

drm/i915/icl: Don't update enabled dbuf slices struct until updated in hw

Do not update number of enabled dbuf slices in dev_priv struct until we
actually enable/disable dbuf slice in hw. This is leading to never
updating dbuf slices and resulting in DBuf slice mismatch warning.

Fixes: aa9664ffe863 ("drm/i915/icl: Enable 2nd DBuf slice only when needed")
Reviewed-by: Paulo Zanoni <[email protected]>
Signed-off-by: Mahesh Kumar <[email protected]>
Signed-off-by: Paulo Zanoni <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit 6ceb7277173597eeed8d635e08db51e35235ab21)
Signed-off-by: Jani Nikula <[email protected]>