riscv: export flush_icache_all to modules

riscv: export flush_icache_all to modules

[ Upstream commit 1833e327a5ea1d1f356fbf6ded0760c9ff4b0594 ]

This is needed by LKDTM (crash dump test module), it calls
flush_icache_range(), which on RISC-V turns into flush_icache_all(). On
other architectures, the actual implementation is exported, so follow
that precedence and export it here too.

Fixes build of CONFIG_LKDTM that fails with:
ERROR: "flush_icache_all" [drivers/misc/lkdtm/lkdtm.ko] undefined!

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>