arch/x86: Make X86 stages select ARCH_X86

Also, don't define the default as this results in spurious lines in the
.config.

TEST: Build all boards with where config.h differed with
BUILD_TIMELESS=1 and remained the same

Change-Id: Ic77b696f493d7648f317f0ba0a27fdee5212961e
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/31316
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/asus/p5gc-mx/Kconfig

@@ -17,7 +17,6 @@ if BOARD_ASUS_P5GC_MX
 
 config BOARD_SPECIFIC_OPTIONS
 	def_bool y
-	select ARCH_X86
 	select CPU_INTEL_SOCKET_LGA775
 	select NORTHBRIDGE_INTEL_I945
 	select NORTHBRIDGE_INTEL_SUBTYPE_I945GC

src/mainboard/asus/p5qc/Kconfig

@@ -18,7 +18,6 @@ if BOARD_ASUS_P5QC || BOARD_ASUS_P5Q_PRO || BOARD_ASUS_P5QL_PRO
 
 config BOARD_SPECIFIC_OPTIONS
 	def_bool y
-	select ARCH_X86
 	select CPU_INTEL_SOCKET_LGA775
 	select NORTHBRIDGE_INTEL_X4X
 	select SOUTHBRIDGE_INTEL_I82801JX

src/mainboard/asus/p5qpl-am/Kconfig

@@ -18,7 +18,6 @@ if BOARD_ASUS_P5QPL_AM || BOARD_ASUS_P5G41T_M_LX
 
 config BOARD_SPECIFIC_OPTIONS
 	def_bool y
-	select ARCH_X86
 	select CPU_INTEL_SOCKET_LGA775
 	select NORTHBRIDGE_INTEL_X4X
 	select SOUTHBRIDGE_INTEL_I82801GX

src/mainboard/asus/p8h61-m_pro/Kconfig

@@ -17,7 +17,6 @@ if BOARD_ASUS_P8H61_M_PRO
 
 config BOARD_SPECIFIC_OPTIONS
 	def_bool y
-	select ARCH_X86
 	select BOARD_ROMSIZE_KB_4096
 	select HAVE_ACPI_RESUME
 	select HAVE_ACPI_TABLES