changed UV plane loop filtering for TX_8X8

changed UV plane loop filtering for TX_8X8

In commit 9a1d73d, loop filtering was added for UV 4x4 boundaries
when TX_8X8 is used by a MB. This commit further refined the decision
to be based on the actual transform used for the UV planes. When
UV planes use 4x4 transform, i.e. when prediction mode used is either
I8X8_PRED or SPLITMV, UV planes are filtered on 4x4 boundaries, and no
filtering is applied on 4x4 block boundaries when UV planes use 8X8
transform.

Change-Id: Ibb404face0a1d129b4b4abaf67c55d82e8df8bec