This patch replaces the memory allocation using request_mem_region and
the ioremap by a single call to managed interface devm_ioremap_reource.
The corresponding calls to release_mem_region and iounmap in the probe
and release functions are now unnecessary and are removed. Also a label
is done away with and linux/device.h is added to make sure the devm_*()
outine declarations are unambiguously available.