cpu/x86: Set up a separate stack for APs

APs use a lot less stack, so set up a separate stack for those in .bss.

Now that CPU_INFO_V2 is the only code path that is used, there is no
need to align stacks in c_start.S.

Change-Id: I7a681a2e3003da0400843daa5d6d6180d952abf5
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69123
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
diff --git a/src/cpu/x86/Kconfig b/src/cpu/x86/Kconfig
index 2253e18..7e58175 100644
--- a/src/cpu/x86/Kconfig
+++ b/src/cpu/x86/Kconfig
@@ -202,4 +202,11 @@
 	  However, modern OSes use PAT to control cacheability instead of
 	  using MTRRs.
 
+config AP_STACK_SIZE
+	hex
+	default 0x800
+	help
+	  This is the amount of stack each AP needs. The BSP stack size can be
+	  larger and is set with STACK_SIZE.
+
 endif # ARCH_X86