devices: fs: Support FOPEN_CACHE_DIR
devices: fs: Support FOPEN_CACHE_DIR

Add support for FOPEN_CACHE_DIR so that the guest can cache directory
entries for longer.

BUG=b:150264964
TEST=vm.Virtiofs

Change-Id: Iade67b54084ed72378afa70af9e9e0f7f0bc03e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2105821
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Chirantan Ekbote <35787c0e27de5c48735e07f8324823b765e8bcbc@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm