kasan: Add riscv to KASAN documentation.

Add riscv to the KASAN documentation to mention that riscv
is supporting generic kasan now.
Signed-off-by: Nick Hu <nickhu@andestech.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

Documentation/dev-tools/kasan.rst

@@ -21,8 +21,8 @@ global variables yet.
 
 Tag-based KASAN is only supported in Clang and requires version 7.0.0 or later.
 
-Currently generic KASAN is supported for the x86_64, arm64, xtensa and s390
-architectures, and tag-based KASAN is supported only for arm64.
+Currently generic KASAN is supported for the x86_64, arm64, xtensa, s390 and
+riscv architectures, and tag-based KASAN is supported only for arm64.
 
 Usage
 -----