powerpc: Move most of setup.h out of uapi

Most of setup.h should not be exported to userspace, so move it
back. All we are left with is the asm-generic include to pick
up the COMMAND_LINE_SIZE define.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>