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

[Angel Pons (Code Review)]

Attention is currently required from: Nico Huber, Furquan Shaikh, Jamie Ryu, Wonkyu Kim, Paul Menzel, Subrata Banik, Raj Astekar, Patrick Rudolph.
Angel Pons has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/51723 )

Change subject: *x86: Support x2apic mode
......................................................................

Patch Set 6:

(5 comments)

Commit Message:

https://review.coreboot.org/c/coreboot/+/51723/comment/e73c6659_b379e705 
PS6, Line 21: cat /proc/cpuinfo | grep "apicid"
> No need to use cat. ;-) […]

I don't like the grep-only approach, especially when I want to change what I'm grepping for. I prefer to put the path first.

File src/cpu/x86/lapic/lapic_cpu_init.c:

https://review.coreboot.org/c/coreboot/+/51723/comment/54f935db_7e689677 
PS6, Line 355: 			LAPIC_DM_INIT | LAPIC_INT_LEVELTRIG, id);
No need to break the line here.

File src/cpu/x86/mp_init.c:

https://review.coreboot.org/c/coreboot/+/51723/comment/3750ada8_0f86ee54 
PS6, Line 458: 	} else {
Return 0 in the if-block and drop the `else`? This way, you don't need to reindent everything.

https://review.coreboot.org/c/coreboot/+/51723/comment/6aff1b80_9c002745 
PS6, Line 678: 	} else {
Simpler:

if (is_x2apic_mode()) {
    x2apic_send_ipi(LAPIC_DM_SMI | LAPIC_INT_LEVELTRIG, lapicid());
    return;
 }

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

https://review.coreboot.org/c/coreboot/+/51723/comment/3c6f407d_603a2028 
PS6, Line 99: #define		X2APIC_LAPIC_ID		(X2APIC_MSR_BASE_ADDRESS | (LAPIC_ID >> 4))
These definitions are misplaced (they're not fields in LAPIC_TDCR, not even LAPIC registers)