x86: apic.c declare pic_mode before they get used

Impact: cleanup, avoid sparse warning

In asm/mpspec.h moved out pic_mode from CONFIG_X86_32 as it is common
for both 32 and 64 bit.

Fixes this sparse warning for x86_64:

  arch/x86/kernel/apic.c:128:5: warning: symbol 'pic_mode' was not declared. Should it be static?

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>