dmaengine: sa11x0: Mark PM functions as __maybe_unused

Without CONFIG_PM_SLEEP, the runtime suspend/resume functions
are unused, producing a warning:

../drivers/dma/sa11x0-dma.c:1042:12: error: 'sa11x0_dma_resume' defined but not used
../drivers/dma/sa11x0-dma.c:1004:12: error: 'sa11x0_dma_suspend' defined but not used

Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Link: https://lore.kernel.org/r/20211026020508.550-1-caihuoqing@baidu.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>