x86 setup: use X86_CR0_PE macro instead of hard-coded constant

To set CR0.PE, use the X86_CR0_PE macro defined in
<asm/processor-flags.h> instead of hardcoding it as a constant (1).

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>