o encode need for A4 bus space tag hackery according to the memory
address; checking for "uart" breaks down with the GPS chip support
which is also a uart but does not require the same hackery
o encode the correct memory window instead of carving up all of i/o
space, potentially with a larger window than a device should have;
this likely should be handled in the drivers by using a proper bus
alloc call but since some drivers depend on the bus support to figure
this out we cannot simply mod them
o add optional GPS and RS485 support (conditionally as the support
isn't ready yet)
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