src: Introduce `ARCH_ALL_STAGES_X86`

Introduce the `ARCH_ALL_STAGES_X86` Kconfig symbol to automatically
select the per-stage arch options. Subsequent commits will leverage
this to allow choosing between 32-bit and 64-bit coreboot where all
stages are x86. AMD Picasso and AMD Cezanne are the only exceptions
to this rule: they disable `ARCH_ALL_STAGES_X86` and explicitly set
the per-stage arch options accordingly.

Change-Id: Ia2ddbae8c0dfb5301352d725032f6ebd370428c9
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55759
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
diff --git a/src/soc/amd/cezanne/Kconfig b/src/soc/amd/cezanne/Kconfig
index 78db12f..7dd3447 100644
--- a/src/soc/amd/cezanne/Kconfig
+++ b/src/soc/amd/cezanne/Kconfig
@@ -70,6 +70,9 @@
 	select X86_AMD_FIXED_MTRRS
 	select X86_AMD_INIT_SIPI
 
+config ARCH_ALL_STAGES_X86
+	default n
+
 config SOC_AMD_COMMON_BLOCK_UCODE_SIZE
 	default 5568