arch/x86: Move prologue to .init section

For arch/x86 the realmode part has to be located within the same 64
KiB as the reset vector. Some older intel platforms also require 4 KiB
alignment for _start16bit.

To enforce the above, and to separate required parts of .text without
matching *(.text.*) rules in linker scripts, tag the pre-C environment
assembly code with section .init directive.

Description of .init section for ELF:

This section holds executable instructions that contribute to the
process initialization code. When a program starts to run, the
system arranges to execute the code in this section before calling the
main program entry point (called main for C programs).

Change-Id: If32518b1c19d08935727330314904b52a246af3c
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47599
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/cpu/intel/car/p4-netburst/cache_as_ram.S b/src/cpu/intel/car/p4-netburst/cache_as_ram.S
index 4e365384..103d9e9 100644
--- a/src/cpu/intel/car/p4-netburst/cache_as_ram.S
+++ b/src/cpu/intel/car/p4-netburst/cache_as_ram.S
@@ -8,6 +8,7 @@
 /* Macro to access Local APIC registers at default base. */
 #define LAPIC(x)		$(LAPIC_DEFAULT_BASE | LAPIC_ ## x)
 
+.section .init
 .global bootblock_pre_c_entry
 
 .code32