src: Move select ARCH_X86 to platforms

To generalise the choice of 32-bit or 64-bit coreboot on x86 hardware,
have platforms select `ARCH_X86` directly instead of through per-stage
Kconfig options, effectively reversing the dependency order.

Change-Id: If15436817ba664398055e9efc6c7c656de3bf3e4
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55758
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>

src/soc/amd/picasso/Kconfig

@@ -13,6 +13,7 @@ config CPU_SPECIFIC_OPTIONS
 	select ARCH_VERSTAGE_X86_32 if !VBOOT_STARTS_BEFORE_BOOTBLOCK
 	select ARCH_ROMSTAGE_X86_32
 	select ARCH_RAMSTAGE_X86_32
+	select ARCH_X86
 	select RESET_VECTOR_IN_RAM
 	select X86_AMD_FIXED_MTRRS
 	select X86_AMD_INIT_SIPI