arch: Move NEEDS_MANUAL_RELOC symbol to Kconfig

CONFIG_NEEDS_MANUAL_RELOC macro was out of Kconfig. Move it there to be
able to use compile-time checks to reduce the number of build paths.

Fixes: f9a882438966 ("dm: core: Convert #ifdef to if() in root.c") for Microblaze
Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>