riscv: Select HAVE_ARCH_USERFAULTFD_MINOR

This allocates the VM flag needed to support the userfaultfd minor fault
functionality. Because the flag bit is >= bit 32, it can only be enabled
for 64-bit kernels. See commit 7677f7fd8be7 ("userfaultfd: add minor
fault registration mode") for more information.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Link: https://lore.kernel.org/r/20230624060321.3401504-1-samuel.holland@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/Kconfig

@@ -100,6 +100,7 @@ config RISCV
 	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
+	select HAVE_ARCH_USERFAULTFD_MINOR if 64BIT && USERFAULTFD
 	select HAVE_ARCH_VMAP_STACK if MMU && 64BIT
 	select HAVE_ASM_MODVERSIONS
 	select HAVE_CONTEXT_TRACKING_USER