drm/msm/gpu: Avoid -Wunused-function with !CONFIG_PM_SLEEP

When building with CONFIG_PM=y and CONFIG_PM_SLEEP=n (such as ARCH=riscv
allmodconfig), the following warnings/errors occur:

  drivers/gpu/drm/msm/adreno/adreno_device.c:679:12: error: 'adreno_system_resume' defined but not used [-Werror=unused-function]
    679 | static int adreno_system_resume(struct device *dev)
        |            ^~~~~~~~~~~~~~~~~~~~
  drivers/gpu/drm/msm/adreno/adreno_device.c:655:12: error: 'adreno_system_suspend' defined but not used [-Werror=unused-function]
    655 | static int adreno_system_suspend(struct device *dev)
        |            ^~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

These functions are only used in SET_SYSTEM_SLEEP_PM_OPS(), which
evaluates to empty when CONFIG_PM_SLEEP is not set, making these
functions unused.

To resolve this, use the SYSTEM_SLEEP_PM_OPS() and RUNTIME_PM_OPS()
macros, which were introduced in commit 1a3c7bb0 ("PM: core: Add new
*_PM_OPS macros, deprecate o...