ARM: highbank: add missing include

highbank_pm_init() is declared in core.h this is not included in the
file that defines it.

arch/arm/mach-highbank/pm.c:43:13: error: no previous prototype for 'highbank_pm_init'

Acked-by: Andre Przywara <andre.przywara@arm.com>
Link: https://lore.kernel.org/r/20230516153109.514251-4-arnd@kernel.org


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