ARM: 7675/1: amba: tegra-ahb: Fix build error w/ PM_SLEEP w/o PM_RUNTIME

Make this depend on CONFIG_PM. This protection is necessary to not
cause any build errors with any combination of PM features especially
when supporting a new SoC where each PM features are being enabled
one-by-one during its depelopment.

Signed-off-by: Hiroshi Doyu <hdoyu@nvidia.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>