drivers: base: refactor add_memory_section() to add_memory_block()

Right now memory_dev_init() maintains the memory block pointer
between iterations of add_memory_section().  This is nasty.

This patch refactors add_memory_section() to become add_memory_block().
The refactoring pulls the section scanning out of memory_dev_init()
and simplifies the signature.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>