Change in coreboot[master]: src/*/x86 : Support x2apic mode

[Wonkyu Kim (Code Review)]

Attention is currently required from: Furquan Shaikh, Jamie Ryu, Ravishankar Sarawadi, Subrata Banik, Srinidhi N Kaushik, Raj Astekar, Patrick Rudolph.
Wonkyu Kim has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/51723 )

Change subject: src/*/x86 : Support x2apic mode
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Patch Set 5:

(1 comment)

File src/include/cpu/x86/lapic.h:

https://review.coreboot.org/c/coreboot/+/51723/comment/37253ceb_ba55e3a6 
PS5, Line 14: LAPIC_BASE_MSR
> That's Architecture MSR from IA32 and shall be generic? In Vol 4 2-4 of Intel SDM. […]

Yes, it should be generic and we already use this in existing enable_lapic function.
static inline void enable_lapic(void)
{
    msr_t msr;
    msr = rdmsr(LAPIC_BASE_MSR);
    msr.hi &= 0xffffff00;
    msr.lo &= ~LAPIC_BASE_MSR_ADDR_MASK;
    msr.lo |= LAPIC_DEFAULT_BASE;
    msr.lo |= LAPIC_BASE_MSR_ENABLE;
    wrmsr(LAPIC_BASE_MSR, msr);
}