x86: move calling z_loapic_enable into z_x86_prep_c

This moves calling z_loapic_enable() from crt0.S into
z_x86_prep_c(). This is done so we can move BSS clearing
and data section copying inside z_x86_prep_c() as
these are needed before calling z_loapic_enable().

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

arch/x86/core/ia32/crt0.S

@@ -224,13 +224,6 @@ __csSet:
 	movl %eax, %cr0
 #endif /* CONFIG_X86_MMU */
 
-#ifdef CONFIG_LOAPIC
-	/* For BSP, cpu_number is 0 */
-	xorl	%eax, %eax
-	pushl	%eax
-	call	z_loapic_enable
-#endif
-
 	pushl	%ebx		/* pointer to multiboot info, or NULL */
 	call	z_x86_prep_c	/* enter kernel; never returns */
 

arch/x86/core/intel64/cpu.c

@@ -163,8 +163,19 @@ FUNC_NORETURN void z_x86_cpu_init(struct x86_cpuboot *cpuboot)
 {
 	x86_sse_init(NULL);
 
+#if CONFIG_MP_NUM_CPUS > 1
 	/* The internal cpu_number is the index to x86_cpuboot[] */
-	z_loapic_enable((unsigned char)(cpuboot - x86_cpuboot));
+	unsigned char cpu_num = (unsigned char)(cpuboot - x86_cpuboot);
+
+	if (cpu_num > 0) {
+		/*
+		 * For CPU #0, z_loapic_enable(0) will be done
+		 * inside z_x86_prep_c() so there is no need to do it
+		 * here.
+		 */
+		z_loapic_enable(cpu_num);
+	}
+#endif
 
 #ifdef CONFIG_USERSPACE
 	/* Set landing site for 'syscall' instruction */

arch/x86/core/prep_c.c

@@ -22,6 +22,10 @@ FUNC_NORETURN void z_x86_prep_c(void *arg)
 
 	_kernel.cpus[0].nested = 0;
 
+#if defined(CONFIG_LOAPIC)
+	z_loapic_enable(0);
+#endif
+
 #ifdef CONFIG_X86_VERY_EARLY_CONSOLE
 	z_x86_early_serial_init();
 #endif