perf: arm_cspmu: Fix modular builds due to missing MODULE_LICENSE()s

Building an arm64 allmodconfig target results in the following failure
from modpost:

  | ERROR: modpost: missing MODULE_LICENSE() in drivers/perf/arm_cspmu/arm_cspmu.o
  | ERROR: modpost: missing MODULE_LICENSE() in drivers/perf/arm_cspmu/nvidia_cspmu.o
  | make[1]: *** [scripts/Makefile.modpost:126: Module.symvers] Error 1
  | make: *** [Makefile:1944: modpost] Error 2

Add the missing MODULE_LICENSE() macros, following the license of the
source files and symbol exports.

Signed-off-by: Will Deacon <will@kernel.org>