spi: bcm-qspi: fix suspend/resume #ifdef

The two power management functions are define inside of an #ifdef
but referenced unconditionally, which is obviously broken when
CONFIG_PM_SLEEP is not set:

drivers/spi/spi-bcm-qspi.c:1300:13: error: 'bcm_qspi_suspend' undeclared here (not in a function)
drivers/spi/spi-bcm-qspi.c:1301:13: error: 'bcm_qspi_resume' undeclared here (not in a function)

This replaces the #ifdef with a __maybe_unused annotation that lets
the compiler figure out whether to drop the functions itself,
and uses SIMPLE_DEV_PM_OPS() to refer to the functions.

This will also fill the freeze/thaw/poweroff/restore callback
pointers in addition to suspend/resume, but as far as I can tell,
this is what we want.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: fa236a7e

 ("spi: bcm-qspi: Add Broadcom MSPI driver")
Signed-off-by: Mark Brown <broonie@kernel.org>