x86: APIC: Make apic_verbosity unsigned

As a microoptimisation, make apic_verbosity unsigned.  This will make
apic_printk(APIC_QUIET, ...) expand into just printk(...) with the
surrounding condition and a reference to apic_verbosity removed.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>