arch/x86,cpu/x86,lib/thread: Remove usage of cpu_info from lib/thread

We only ever start and execute threads on the BSP. By explicitly
checking to see if the CPU is the BSP we can remove the dependency on
cpu_info. With this change we can in theory enable threads in all
stages.

BUG=b:194391185, b:179699789
TEST=Boot guybrush to OS and verify coop multithreading still works

Suggested-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Change-Id: Iea4622d52c36d529e100b7ea55f32c334acfdf3e
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58199
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/cpu/x86/cpu_info.S.inc

@@ -2,9 +2,6 @@
 
 /* Push struct cpu_info */
 .macro push_cpu_info index=$0
-#if CONFIG(COOP_MULTITASKING)
-	push	$0	/* *thread */
-#endif
 	push	\index	/* index */
 	push	$0	/* *cpu */
 .endm