x86/platform: Avoid missing-prototype warnings for OLPC

There are two functions in the olpc platform that have no prototype:

arch/x86/platform/olpc/olpc_dt.c:237:13: error: no previous prototype for 'olpc_dt_fixup' [-Werror=missing-prototypes]
arch/x86/platform/olpc/olpc-xo1-pm.c:73:26: error: no previous prototype for 'xo1_do_sleep' [-Werror=missing-prototypes]

The first one should just be marked 'static' as there are no other
callers, while the second one is called from assembler and is
just a false-positive warning that can be silenced by adding a
prototype.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Link: https://lore.kernel.org/all/20230516193549.544673-21-arnd%40kernel.org