dmaengine: cppi41: mark PM functions as __maybe_unused

When CONFIG_PM_SLEEP is disabled, we get a build error in
the cppi41 dmaengine driver, since the runtime-pm functions
are hidden within the wrong #ifdef:

drivers/dma/cppi41.c:1158:21: error: 'cppi41_runtime_suspend' undeclared here (not in a function)

This removes the #ifdef and instead uses __maybe_unused
annotations that cannot have this problem.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: fdea2d09 ("dmaengine: cppi41: Add basic PM runtime support")
Signed-off-by: Vinod Koul <vinod.koul@intel.com>