spi: fsl-lpspi: Fix build warning when !CONFIG_PM

spi: fsl-lpspi: Fix build warning when !CONFIG_PM

Add #ifdef CONFIG_PM guard to fix build warning when !CONFIG_PM
drivers/spi/spi-fsl-lpspi.c:810:12: warning: ‘fsl_lpspi_runtime_suspend’ defined but not used [-Wunused-function]
 static int fsl_lpspi_runtime_suspend(struct device *dev)
            ^~~~~~~~~~~~~~~~~~~~~~~~~
drivers/spi/spi-fsl-lpspi.c:789:12: warning: ‘fsl_lpspi_runtime_resume’ defined but not used [-Wunused-function]
 static int fsl_lpspi_runtime_resume(struct device *dev)
            ^~~~~~~~~~~~~~~~~~~~~~~~

Fixes: 944c01a889d9 ("spi: lpspi: enable runtime pm for lpspi")
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@kernel.org>