Reworked DMA address sizes and SGListMMU

Parameterized SGListMMU over physical address size and updated its interface so that it maps all addresses supported by the interface.

Defined typedef DmaAddrSize, which is currently 24. This can be increased when we need to, perhaps via `ifdef.

Updated AxiRDMA accordingly, though it is still using 40 bit physical addresses on all platforms.

Change-Id: Ib9715efdd9e0ece6b910d23122177609338485fd