tools/bootconfig: Define memblock_free_ptr() to fix build error

The lib/bootconfig.c file is shared with the 'bootconfig' tooling, and
as a result, the changes incommit 77e02cf5 ("memblock: introduce
saner 'memblock_free_ptr()' interface") need to also be reflected in the
tooling header file.

So define the new memblock_free_ptr() wrapper, and remove unused __pa()
and memblock_free().

Fixes: 77e02cf5 ("memblock: introduce saner 'memblock_free_ptr()' interface")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>