drivers: base: unshare add_memory_section() from hotplug

add_memory_section() is currently called from both boot time and run
time via hotplug and there is a lot of nastiness to allow for shared
code including an enum parameter to convey the calling context to
add_memory_section().

This patch is the first step in breaking up the messy code sharing by
pulling the hotplug path for add_memory_section() directly into
register_new_memory().

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