armv7m: Make bitband device take the address space to access

Instead of the bitband device doing a cpu_physical_memory_read/write,
make it take a MemoryRegion which specifies where it should be
accessing, and use address_space_read/write to access the
corresponding AddressSpace.

Since this entails pretty much a rewrite, convert away from
old_mmio in the process.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 1487604965-23220-8-git-send-email-peter.maydell@linaro.org