perf: starfive: Only allow COMPILE_TEST for 64-bit architectures

The kbuild robot exploded while wasting its time building the Starfive
PMU driver for the 32-bit PA-RISC and Hexagon architectures.

Adjust the Kconfig dependencies so that COMPILE_TEST is only applicable
for 64-bit architectures (which implement writeq()).

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Will Deacon <will@kernel.org>