xtensa: enable ARCH_HAS_DEBUG_VM_PGTABLE

xtensa kernels successfully build and run with
CONFIG_DEBUG_VM_PGTABLE=y, enable arch support for it.
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

Documentation/features/debug/debug-vm-pgtable/arch-support.txt

@@ -27,5 +27,5 @@
     |       sparc: | TODO |
     |          um: | TODO |
     |         x86: |  ok  |
-    |      xtensa: | TODO |
+    |      xtensa: |  ok  |
     -----------------------

arch/xtensa/Kconfig

@@ -4,6 +4,7 @@ config XTENSA
 	select ARCH_32BIT_OFF_T
 	select ARCH_HAS_BINFMT_FLAT if !MMU
 	select ARCH_HAS_CURRENT_STACK_POINTER
+	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DMA_PREP_COHERENT if MMU
 	select ARCH_HAS_SYNC_DMA_FOR_CPU if MMU
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE if MMU