Use Start/End addressing instead of Base/Mask

Using Base/Mask addressing makes it impossible to have memory regions
which are not aligned to their size, which will not work for our
application. For example, we want to have zeropage and stack in SRAM but
the rest of the slaves in a sdram or ddr ram. With the old addressing
scheme, this is impossible since the first memory area is 512 bytes,
which means the proceding memory area can only be 512 bytes max.

The other solution to this is to have these smaller memory areas handled
in the address translater, but I would rather have the ability to have
arbitrarily sized and aligned memory areas in the crossbar. If this
impacts performance too much then I guess it can be re-evaluated