powerpc/512x: Fix missing prototype warnings

The mpc512x_defconfig build fails with:

  arch/powerpc/platforms/512x/mpc5121_ads_cpld.c:142:1: error: no previous prototype for ‘mpc5121_ads_cpld_map’ [-Werror=missing-prototypes]
  142 | mpc5121_ads_cpld_map(void)
      | ^~~~~~~~~~~~~~~~~~~~
  arch/powerpc/platforms/512x/mpc5121_ads_cpld.c:157:1: error: no previous prototype for ‘mpc5121_ads_cpld_pic_init’ [-Werror=missing-prototypes]
  157 | mpc5121_ads_cpld_pic_init(void)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~

There are prototypes for these functions but the header they are in is
not included by mpc5121_ads_cpld.c. Include it to fix the build error.

Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231129131919.2528517-3-mpe@ellerman.id.au