allocates kva space from the top down for the device mappings and builds
entries in an internal table which is automatically used later by
arm_devmap_bootstrap(). The platform code just calls the new
arm_devmap_add_entry() function as many times as it needs to (up to 32
entries allowed; most platforms use 2 or 3 at most).
There is also a new arm_devmap_lastaddr() function that returns the lowest
kva address allocated; this can be used to implement initarm_lastaddr()
which is used to initialize vm_max_kernel_address.
The new code is based on a similar concept developed for the imx family
SoCs recently. They will soon be converted to use this new common code.
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