arch|cpu/x86: Add Kconfig option for x86 reset vector

Prepare for an implementation supporting the reset vector in RAM and
not the traditional 0xfffffff0.  Add a Kconfig symbol that can be used
in place of hardcoded values.

Change-Id: I6a814f7179ee4251aeeccb2555221616e944e03d
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37485
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/arch/x86/Kconfig

@@ -87,6 +87,16 @@ config AP_IN_SIPI_WAIT
 	default n
 	depends on ARCH_X86 && SMP
 
+config X86_RESET_VECTOR
+	hex
+	depends on ARCH_X86
+	default 0xfffffff0
+	help
+	  Specify the location of the x86 reset vector.  In traditional devices
+	  this must match the architectural reset vector to produce a bootable
+	  image.  Nontraditional designs may use this to position the reset
+	  vector into its desired location.
+
 config RESET_VECTOR_IN_RAM
 	bool
 	depends on ARCH_X86

src/arch/x86/failover.ld

@@ -14,7 +14,7 @@
 ENTRY(_start)
 
 MEMORY {
-	rom : ORIGIN = 0xffff0000, LENGTH = 64K
+	rom : ORIGIN = CONFIG_X86_RESET_VECTOR - 0xfff0, LENGTH = 64K
 }
 
 TARGET(binary)

src/arch/x86/id.ld

@@ -12,7 +12,7 @@
  */
 
 SECTIONS {
-	. = (0xffffffff - CONFIG_ID_SECTION_OFFSET) - (__id_end - __id_start) + 1;
+	. = (CONFIG_X86_RESET_VECTOR - CONFIG_ID_SECTION_OFFSET) - (__id_end - __id_start) + 0x10;
 	.id (.): {
 		KEEP(*(.id))
 	}

src/arch/x86/memlayout.ld

@@ -50,7 +50,7 @@ SECTIONS
 	#include EARLY_MEMLAYOUT
 #elif ENV_BOOTBLOCK
 	/* arch/x86/bootblock.ld contains the logic for the ROMCC_BOOTBLOCK linking. */
-	BOOTBLOCK(0xffffffff - CONFIG_C_ENV_BOOTBLOCK_SIZE + 1,
+	BOOTBLOCK(CONFIG_X86_RESET_VECTOR - CONFIG_C_ENV_BOOTBLOCK_SIZE + 0x10,
 			CONFIG_C_ENV_BOOTBLOCK_SIZE)
 
 	#include EARLY_MEMLAYOUT