memory-hotplug: create /sys/firmware/memmap entry for new memory

A memmap is a directory in sysfs which includes 3 text files: start, end
and type.  For example:

start: 	0x100000
end:	0x7e7b1cff
type:	System RAM

Interface firmware_map_add was not called explicitly.  Remove it and add
function firmware_map_add_hotplug as hotplug interface of memmap.

Each memory entry has a memmap in sysfs, When we hot-add new memory, sysfs
does not export memmap entry for it.  We add a call in function add_memory
to function firmware_map_add_hotplug.

Add a new function add_sysfs_fw_map_entry() to create memmap entry, it
will be called when initialize memmap and hot-add memory.

[akpm@linux-foundation.org: un-kernedoc a no longer kerneldoc comment]
Signed-off-by: Shaohui Zheng <shaohui.zheng@intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>