more pipelining of SGList

Change-Id: I231bc6aa301a8fc2bed138a1df2743feb10f715c
pipeline computation of the readReq/writeReq guards in DMA buffers

Change-Id: I11e120d4be7a0992c03cb111684232d7ce674a21
make sure all uses of FCLK come from the BUFG

Change-Id: I719554846be2e418470e2056d5179f2b62df1ebf
pipeline the region() method

Change-Id: Ifdae47396ac3225096b4fda574ffd91ce4630819