perf/arm_cspmu: Fix missing io.h include

perf/arm_cspmu: Fix missing io.h include

Adding the writel() calls needs io.h, which apparently gets
transiently included somewhere on arm64, but not elsewhere.

Fixes: 6de0298a3925 ("perf/arm_cspmu: Generalise event filtering")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202503150649.Dol8RBSh-lkp@intel.com/
Closes: https://lore.kernel.org/oe-kbuild-all/202503152245.cAG4FMfi-lkp@intel.com/
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/657935ca177024ad08d5ec6f85e8faf75f82cf65.1742212833.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>