util: Extract flush_icache_range to cacheflush.c

util: Extract flush_icache_range to cacheflush.c

This has been a tcg-specific function, but is also in use
by hardware accelerators via physmem.c.  This can cause
link errors when tcg is disabled.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Joelle van Dyne <j@getutm.app>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20201214140314.18544-3-richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>