powerpc: add missing MODULE_DESCRIPTION() macros

With ARCH=powerpc, make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in arch/powerpc/kernel/rtas_flash.o
WARNING: modpost: missing MODULE_DESCRIPTION() in arch/powerpc/sysdev/rtc_cmos_setup.o
WARNING: modpost: missing MODULE_DESCRIPTION() in arch/powerpc/platforms/pseries/papr_scm.o
WARNING: modpost: missing MODULE_DESCRIPTION() in arch/powerpc/platforms/cell/spufs/spufs.o
WARNING: modpost: missing MODULE_DESCRIPTION() in arch/powerpc/platforms/cell/cbe_thermal.o
WARNING: modpost: missing MODULE_DESCRIPTION() in arch/powerpc/platforms/cell/cpufreq_spudemand.o
WARNING: modpost: missing MODULE_DESCRIPTION() in arch/powerpc/platforms/cell/cbe_powerbutton.o

Add the missing invocation of the MODULE_DESCRIPTION() macro to all
files which have a MODULE_LICENSE().

This includes 85xx/t1042rdb_diu.c and chrp/nvram.c which, although
they did not produce a warning with the powerpc allmodconfig
configuration, may cause this warning with other configurations.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240615-md-powerpc-arch-powerpc-v1-1-ba4956bea47a@quicinc.com