ARM: imx: add missing include

imx25_pm_init() is declared in common.h but this is not included
before its definition:

arch/arm/mach-imx/pm-imx25.c:31:13: error: no previous prototype for 'imx25_pm_init'

Link: https://lore.kernel.org/r/20230516153109.514251-5-arnd@kernel.org


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