ARM: rockchip: make rockchip_suspend_init conditional

If CONFIG_PM_SLEEP is disabled, we get a build error for rockchips:

arch/arm/mach-rockchip/built-in.o: In function `rockchip_dt_init':
:(.init.text+0x1c): undefined reference to `rockchip_suspend_init'

This adds an inline alternative for that case.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Cc: linux-rockchip@lists.infradead.org