x86/apic: Use non-atomic operations when possible

Using __clear_bit() and __cpumask_clear_cpu() is more efficient than using
their atomic counterparts.

Use them when atomicity is not needed, such as when manipulating bitmasks
that are on the stack.

Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20190613064813.8102-10-namit@vmware.com