Nano HPO: support more functions in tf.*

[shane-huang]

Problem:

Currenly only tf.cast is supported in bigdl.nano.tf. There're more functions available in tf.*, refer to https://www.tensorflow.org/api_docs/python/tf#functions_2. User may need to use other functions in tf namespace.

Solution:

Extend the TF_FUNCS processing at https://github.com/intel-analytics/BigDL/blob/main/python/nano/src/bigdl/nano/automl/hpo/config.py#L42. Try use generic ways to detect the functions defined in the namespace instead of listing one by one.