arch/x86/kernel/acpi/boot.c: removed duplicated #include

Removed duplicated include file <asm/genapic.h> in
arch/x86/kernel/acpi/boot.c.

Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>