bus_space_(write|read)_X cleanup

[Oleksandr Tymoshenko]

Hello,

One of the practices in ARM codebase that caught my eye recently
was using bus_space_write_4 (and read) where it's not strictly required.

The way it usually goes: memory resource is allocated in driver's attach
method then busspace tag/handle obtained by calling rman_get_bustag
and rman_get_bushandle, stored in softc and used as a parameters  of
bus_space calls. No other operations on handle/tag are performed.

There are bus_read/bus_write wrappers that provide cleaner API
and reduce code complexity. I believe it might be worth going through
the code and fixing cases of excessive use of bus_space_  functions.

Unless I missed something.