riscv: Unconditionnally select KASAN_VMALLOC if KASAN

If KASAN is enabled, VMAP_STACK depends on KASAN_VMALLOC so enable
KASAN_VMALLOC with KASAN so that we can enable VMAP_STACK by default.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20230203075232.274282-7-alexghiti@rivosinc.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>