Allow hidl_vec = initializer list

Currently, a hidl vector can be constructed using an initializer list, but
it cannot be made equal to an initializer list.
Add the missing operator here to allow for simpler usage.

Test: atest libhidl_test
Bug: 117935272
Change-Id: Id21e9cafee754968a7300a3d7bc85481d32dcc3a
2 files changed