Revert "CHROMIUM: riscv: Hack riscv arch flags"

This reverts commit a15a310.

Reason for revert: Updating to GCC 14.2

Original change's description:
> CHROMIUM: riscv: Hack riscv arch flags
>
> When using the coreboot-sdk, don't append zicsr or zifencei to the
> -march flag. Once coreboot-sdk supports isa-spec=20191213 or upgrades
> to gcc 12, then revert this cl.
>
> BRANCH=None
> BUG=b:245409408
> TEST=zmake build -a
>
> Signed-off-by: Jeremy Bettis <jbettis@google.com>
> Change-Id: Ia712f6d97dace15bdb5cb7d36bbf864db046c0d0
> Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/3884659
> Tested-by: Jeremy Bettis <jbettis@chromium.org>
> Commit-Queue: Jeremy Bettis <jbettis@chromium.org>
> Reviewed-by: Aaron Massey <aaronmassey@google.com>

BUG=b:245409408

Change-Id: I6b0ab35c43fac0f635bc8bf3a5da5f960dd77508
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5949063
Commit-Queue: Jonathon Murphy <jpmurphy@google.com>
Reviewed-by: Jeremy Bettis <jbettis@chromium.org>
Tested-by: Jonathon Murphy <jpmurphy@google.com>

cmake/compiler/gcc/target_riscv.cmake

@@ -45,15 +45,12 @@ if(CONFIG_RISCV_ISA_EXT_C)
     string(CONCAT riscv_march ${riscv_march} "c")
 endif()
 
-# TODO(b/245409408): Revert this when coreboot-sdk supports isa-spec=20191213
-if (NOT ZEPHYR_TOOLCHAIN_VARIANT STREQUAL "coreboot-sdk")
-    if(CONFIG_RISCV_ISA_EXT_ZICSR)
-        string(CONCAT riscv_march ${riscv_march} "_zicsr")
-    endif()
+if(CONFIG_RISCV_ISA_EXT_ZICSR)
+    string(CONCAT riscv_march ${riscv_march} "_zicsr")
+endif()
 
-    if(CONFIG_RISCV_ISA_EXT_ZIFENCEI)
-        string(CONCAT riscv_march ${riscv_march} "_zifencei")
-    endif()
+if(CONFIG_RISCV_ISA_EXT_ZIFENCEI)
+    string(CONCAT riscv_march ${riscv_march} "_zifencei")
 endif()
 
 if(CONFIG_RISCV_ISA_EXT_ZBA)