arm64: remove wrong CONFIG_PROC_SYSCTL ifdef

The sysfs cpu_capacity entry for each CPU has nothing to do with
PROC_FS, nor it's in /proc/sys path.

Remove such ifdef.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Reported-and-suggested-by: Sudeep Holla <sudeep.holla@arm.com>
Fixes: be8f185d ('arm64: add sysfs cpu_capacity attribute')
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>