arm64: mm: use ARCH_HAS_DEBUG_WX instead of arch defined

Extract DEBUG_WX to mm/Kconfig.debug for shared use.  Change to use
ARCH_HAS_DEBUG_WX instead of DEBUG_WX defined by arch port.
Signed-off-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Link: http://lkml.kernel.org/r/e19709e7576f65e303245fe520cad5f7bae72763.1587455584.git.zong.li@sifive.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm64/Kconfig

@@ -9,6 +9,7 @@ config ARM64
 	select ACPI_MCFG if (ACPI && PCI)
 	select ACPI_SPCR_TABLE if ACPI
 	select ACPI_PPTT if ACPI
+	select ARCH_HAS_DEBUG_WX
 	select ARCH_BINFMT_ELF_STATE
 	select ARCH_HAS_DEBUG_VIRTUAL
 	select ARCH_HAS_DEVMEM_IS_ALLOWED

arch/arm64/Kconfig.debug

@@ -23,35 +23,6 @@ config ARM64_RANDOMIZE_TEXT_OFFSET
 	  of TEXT_OFFSET and platforms must not require a specific
 	  value.
 
-config DEBUG_WX
-	bool "Warn on W+X mappings at boot"
-	select PTDUMP_CORE
-	---help---
-	  Generate a warning if any W+X mappings are found at boot.
-
-	  This is useful for discovering cases where the kernel is leaving
-	  W+X mappings after applying NX, as such mappings are a security risk.
-	  This check also includes UXN, which should be set on all kernel
-	  mappings.
-
-	  Look for a message in dmesg output like this:
-
-	    arm64/mm: Checked W+X mappings: passed, no W+X pages found.
-
-	  or like this, if the check failed:
-
-	    arm64/mm: Checked W+X mappings: FAILED, <N> W+X pages found.
-
-	  Note that even if the check fails, your kernel is possibly
-	  still fine, as W+X mappings are not a security hole in
-	  themselves, what they do is that they make the exploitation
-	  of other unfixed kernel bugs easier.
-
-	  There is no runtime or memory usage effect of this option
-	  once the kernel has booted up - it's a one time check.
-
-	  If in doubt, say "Y".
-
 config DEBUG_EFI
 	depends on EFI && DEBUG_INFO
 	bool "UEFI debugging"