PM/devfreq: governor: add missing MODULE_DESCRIPTION() macros

PM/devfreq: governor: add missing MODULE_DESCRIPTION() macros

make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/devfreq/governor_simpleondemand.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/devfreq/governor_performance.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/devfreq/governor_powersave.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/devfreq/governor_userspace.o

Add all missing invocations of the MODULE_DESCRIPTION() macro.

Link: https://lore.kernel.org/lkml/20240605-md-drivers-devfreq-v1-1-d01ae91b907e@quicinc.com/
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>