arm: armv8: invalidate dcache entries on dcache_enable

arm: armv8: invalidate dcache entries on dcache_enable

In dcache_enable, currently the dcache entries are only invalidated when
the MMU is not enabled. This causes issues when dcache_enable is called
with the MMU already configured, in such cases the existing dcache
entries are not flushed which might result in un-expected behavior.

This patch invalidates the cache entries on every call of dcache_enable
before enabling dcache (by setting CR_C). This makes dcache_enable
behave similar to icache_enable as well.

Reviewed-by: Dhruva Gole <d-gole@ti.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Anshul Dalal <anshuld@ti.com>
Tested-by: Wadim Egorov <w.egorov@phytec.de>