riscv: TRANSPARENT_HUGEPAGE: depends on MMU

Fix a Kconfig warning and many build errors:

WARNING: unmet direct dependencies detected for COMPACTION
  Depends on [n]: MMU [=n]
  Selected by [y]:
  - TRANSPARENT_HUGEPAGE [=y] && HAVE_ARCH_TRANSPARENT_HUGEPAGE [=y]

and the subseqent thousands of build errors and warnings.

Fixes: e88b333142 ("riscv: mm: add THP support on 64-bit")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -105,7 +105,7 @@ config RISCV
 	select SYSCTL_EXCEPTION_TRACE
 	select THREAD_INFO_IN_TASK
 	select UACCESS_MEMCPY if !MMU
-	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT
+	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
 
 config ARCH_MMAP_RND_BITS_MIN
 	default 18 if 64BIT