Mark binutils/gdb requirements for RISC-V

Signed-off-by: Alexey Neyman <stilor@att.net>

config/arch/riscv.in

@@ -11,6 +11,8 @@
 ## select ARCH_SUPPORTS_WITH_ARCH
 ## select ARCH_SUPPORTS_WITH_TUNE
 ## select GCC_REQUIRE_7_or_later
+## select BINUTILS_REQUIRE_2_28_or_later
+## select GDB_REQUIRE_8_0_or_later
 
 ## help The RISC-V architecture, as defined by:
 ## help     http://www.riscv.org/