ARM: sa1100: address missing prototype warnings

There are three warnings for mach-sa1100 when building with W=1:

arch/arm/common/sa1111.c:699:1: error: no previous prototype for 'sa1111_configure_smc' [-Werror=missing-prototypes]
  699 | sa1111_configure_smc(struct sa1111 *sachip, int sdram, unsigned int drac,
      | ^~~~~~~~~~~~~~~~~~~~
arch/arm/mach-sa1100/assabet.c:718:13: error: no previous prototype for 'assabet_init_irq' [-Werror=missing-prototypes]
  718 | void __init assabet_init_irq(void)
      |             ^~~~~~~~~~~~~~~~
arch/arm/mach-sa1100/pm.c:126:12: error: no previous prototype for 'sa11x0_pm_init' [-Werror=missing-prototypes]
  126 | int __init sa11x0_pm_init(void)
      |            ^~~~~~~~~~~~~~

The first two are only used locally and can be 'static', while
the last one needs to include the right header.

Link: https://lore.kernel.org/r/20230516153109.514251-12-arnd@kernel.org


Signed-off-by: Arnd Bergmann <arnd@arndb.de>