Nuvoton: Organize file structure

[ccli8]

Description

This PR just organizes file structure and makes no logic change. This is to avoid duplicate when a new target of the same MCU series is added. For example, a new target NUMAKER_IOT_M487 will be added, which shares most code with existent NUMAKER_PFM_M487.

Pull request type

[ ] Fix
[X] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2720
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7676/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Test : SUCCESS

Build number : 2452
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7676/2452

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2356
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7676/