RISC-V: fix riscv64 extension isa problem

RISC-V: fix riscv64 extension isa problem

During building with tizen gcc, the below message is displayed.

[   33s] arch/riscv/lib/cache.c:12: Error: unrecognized opcode `fence.i', extension `zifencei' required
[   33s] make[1]: *** [scripts/Makefile.build:257: arch/riscv/lib/cache.o] Error 1
[   33s] make[1]: *** Waiting for unfinished jobs....
[   33s]   CC      common/miiphyutil.o
[   34s]   CC      boot/image.o
[   34s]   CC      boot/image-board.o

Older gcc doesn't support some isa extensions for riscv.
(Since GCC 11.1, it's supported.)
This patch is refered to below commit of linux-starfive repo.

commit e6303a1c7cf531457aca1ff35f3d3ee38977eca2
Author: Marek Szulc <m.szulc3@samsung.com>
Date:   Fri Aug 19 12:29:48 2022 +0200

    riscv: fix riscv64 unrecognized opcode build error

Change-Id: Ib4f52134bad8d9f1971d4d8fb9f757d2fa9cfb1e
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>