riscv: Make GCC default architecture include zicsr and zifencei

This makes the new version of GCC compatible with older versions
when no -march is specified on the command line

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

configs/riscv64-zephyr-elf.config

@@ -5,7 +5,7 @@ CT_EXPERIMENTAL=y
 CT_ARCH_RISCV=y
 CT_MULTILIB=y
 CT_ARCH_64=y
-CT_ARCH_ARCH="rv32ima"
+CT_ARCH_ARCH="rv32ima_zicsr_zifencei"
 CT_ARCH_ABI="ilp32"
 CT_TARGET_VENDOR="zephyr"
 CT_BINUTILS_SRC_CUSTOM=y