x86/kconfig: Move 64-bit only arch Kconfig selects to 'config X86_64'

These are easier to read when they come next to the X86_64 config.

Note that all remaining 'if X86_64' config options in the generic
section are in principle suitable for activation on 32-bit, but have
not been ported yet.
Reported-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

arch/x86/Kconfig

@@ -21,8 +21,20 @@ config X86_32
 config X86_64
 	def_bool y
 	depends on 64BIT
+	# Options that are inherently 64-bit kernel only:
+	select ARCH_HAS_GIGANTIC_PAGE
+	select ARCH_SUPPORTS_INT128
+	select ARCH_USE_CMPXCHG_LOCKREF
+	select HAVE_ARCH_SOFT_DIRTY
+	select MODULES_USE_ELF_RELA
+	select X86_DEV_DMA_OPS
 
-### Arch settings
+#
+# Arch settings
+#
+# ( Note that options that are marked 'if X86_64' could in principle be
+#   ported to 32-bit as well. )
+#
 config X86
 	def_bool y
 	select ACPI_LEGACY_TABLES_LOOKUP	if ACPI
@@ -35,7 +47,6 @@ config X86
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_FAST_MULTIPLIER
 	select ARCH_HAS_GCOV_PROFILE_ALL
-	select ARCH_HAS_GIGANTIC_PAGE		if X86_64
 	select ARCH_HAS_KCOV			if X86_64
 	select ARCH_HAS_PMEM_API		if X86_64
 	select ARCH_HAS_MMIO_FLUSH
@@ -47,10 +58,8 @@ config X86
 	select ARCH_MIGHT_HAVE_PC_SERIO
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
-	select ARCH_SUPPORTS_INT128		if X86_64
 	select ARCH_SUPPORTS_NUMA_BALANCING	if X86_64
 	select ARCH_USE_BUILTIN_BSWAP
-	select ARCH_USE_CMPXCHG_LOCKREF		if X86_64
 	select ARCH_USE_QUEUED_RWLOCKS
 	select ARCH_USE_QUEUED_SPINLOCKS
 	select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH if SMP
@@ -92,7 +101,6 @@ config X86
 	select HAVE_ARCH_MMAP_RND_BITS		if MMU
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if MMU && COMPAT
 	select HAVE_ARCH_SECCOMP_FILTER
-	select HAVE_ARCH_SOFT_DIRTY		if X86_64
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	select HAVE_ARCH_WITHIN_STACK_FRAMES
@@ -150,7 +158,6 @@ config X86
 	select HAVE_UNSTABLE_SCHED_CLOCK
 	select HAVE_USER_RETURN_NOTIFIER
 	select IRQ_FORCED_THREADING
-	select MODULES_USE_ELF_RELA		if X86_64
 	select OLD_SIGSUSPEND3			if X86_32 || IA32_EMULATION
 	select PERF_EVENTS
 	select RTC_LIB
@@ -161,7 +168,6 @@ config X86
 	select THREAD_INFO_IN_TASK
 	select USER_STACKTRACE_SUPPORT
 	select VIRT_TO_BUS
-	select X86_DEV_DMA_OPS			if X86_64
 	select X86_FEATURE_NAMES		if PROC_FS
 	select HAVE_STACK_VALIDATION		if X86_64
 	select ARCH_USES_HIGH_VMA_FLAGS		if X86_INTEL_MEMORY_PROTECTION_KEYS