Make the bootheader for ppc64 independent from kernel and libc headers.
* add -nostdinc -isystem $gccincludes to not include libc headers
* declare all functions in header files, also the stuff from string.S
* declare some functions static
* use stddef.h to get size_t (hopefully ok)
* remove ppc32-types.h, only elf.h used the __NN types

With further modifications by Paul Mackerras and Stephen Rothwell.

Signed-off-by: Olaf Hering <olh@suse.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>